Cover page

Image Name: Flame Nebula: This collage of images from the Flame Nebula shows a near-infrared light view

from NASA’s Hubble Space Telescope, while the two insets below show the near-infrared view taken by NASA’s

James Webb Space Telescope. Much of the dark, dense gas and dust, as well as the surrounding white clouds

within the Hubble image, have been cleared in the Webb images, giving us a view into a more translucent cloud

pierced by the infrared-producing objects within that are young stars and brown dwarfs. Astronomers used Webb

to take a census of the lowest-mass objects within this star-forming region.

For more information, visit: https://science.nasa.gov/missions/webb/nasas-webb-peers-deeper-into-mysterious-f

lame-nebula/

Managing Editor Chief Editor Editorial Board Correspondence

Ninan Sajeeth Philip Abraham Mulamoottil K Babu Joseph The Chief Editor

Ajit K Kembhavi airis4D

Geetha Paul Thelliyoor - 689544

Arun Kumar Aniyan India

Sindhu G

Journal Publisher Details

Publisher : airis4D, Thelliyoor 689544, India

Website : www.airis4d.com

Email : nsp@airis4d.com

Phone : +919497552476

Editorial

by Fr Dr Abraham Mulamoottil

airis4D, Vol.3, No.5, 2025

www.airis4d.com

With the stunning “Flame Nebula” on the cover

page, this edition starts with the article of Prof. Ajit

Kembhav, ”Black Hole Stories-18: Gravitational Waves

from The Binary Radio Pulsar 1913+16”. The article

details how the binary pulsar system PSR B1913+16

provided the ﬁrst indirect evidence for gravitational

waves, conﬁrming Einstein’s general theory of relativity.

Discovered by Hulse and Taylor in 1974, this system

consists of two neutron stars (1.44 and 1.39 solar masses)

in a tight, elliptical orbit with a perihelion distance

smaller than the Sun’s radius. Precise measurements

of pulse arrival times revealed relativistic eﬀects like

extreme perihelion precession (4.2°/year) and orbital

decay due to energy loss via gravitational waves, with

the orbital period decreasing by 76.5 microseconds

annually—matching Einstein’s predictions with less

than 1

In the article by Abhishek P. S, ”A Brief

Introduction to Plasma Physics”, Plasma, often called

the ”fourth state of matter,” is an ionised gas consisting

of free electrons and ions that exhibit collective

behaviour due to long-range electromagnetic forces.

First termed by Irving Langmuir, plasma forms when

atoms gain enough thermal energy to overcome electron

binding forces, transitioning gradually from gas to

plasma without a distinct phase change. Unlike

neutral matter, plasmas display unique properties

like Debye shielding (screening external electric

ﬁelds over distances larger than the Debye length)

and quasineutrality (macroscopic neutrality despite

microscopic charge separation). They also oscillate

at a characteristic plasma frequency when disturbed.

Plasmas dominate the universe, evident in stars (e.g.,

the Sun’s corona), solar wind, Earth’s magnetosphere

(Van Allen belts), and ionosphere. Applications range

from gas discharges (ﬂuorescent lights) to cutting-

edge technologies like magnetohydrodynamic energy

conversion, ion propulsion for spacecraft, and controlled

thermonuclear fusion—a potential clean energy source

mimicking stellar processes. The study of plasmas

bridges astrophysics (e.g., pulsars, black holes) and

engineering, leveraging their conductive and wave-

sustaining properties for diagnostics and innovation.

The article by Aromal P, ”X-ray Astronomy:

Through Missions” highlights key X-ray astronomy

missions launched in the mid-to-late 2000s, focusing

on Suzaku (ASTRO-EII), AGILE, and MAXI. Japan’s

Suzaku (2005–2015), a collaboration between JAXA

and NASA, featured advanced instruments like the X-ray

Imaging Spectrometer (XIS) and Hard X-ray Detector

(HXD), enabling groundbreaking studies of galaxy

clusters (e.g., the Perseus Cluster’s iron distribution)

and black hole spin measurements. Despite the failure of

its X-ray Spectrometer (XRS), Suzaku paved the way for

future missions. Italy’s AGILE (2007–2024) monitored

gamma-ray and hard X-ray sources with instruments

like SuperAGILE and the Gamma Ray Imager Detector

(GRID), while Japan’s MAXI (2009–present), mounted

on the ISS, conducts all-sky surveys with its Gas Slit

Camera (GSC) and Solid-State Slit Camera (SSC),

discovering transient events like tidal disruption events

(TDEs). Together, these missions expanded our

understanding of high-energy astrophysical phenomena,

from supernova remnants to active galactic nuclei.

In his article ”The Hunt for the Cosmic Radio

Lines of Neutral Hydrogen”, Linn Abraham takes us

to a walk to radio signals and their use in Astronomy.

Karl Jansky accidentally discovered a “steady hiss

type static of unknown origin” in 1932 while studying

interference on transatlantic radio telephone service.

Later, researcher Grote Reber took up the challenge of

building a dedicated radio telescopes in his backyard.

Another researcher, Reber, produced the ﬁrst radio

contour maps of the sky, beautifully outlining the Milky

Way and hints of discrete sources. This opened the

world to the branch of rasio astronomy.

According to the article by Sindhu G, ”Type I

Supernovae: Stellar Explosions Without Hydrogen”,

Type I supernovae, distinguished by their lack of

hydrogen spectral lines, are powerful stellar explosions

that play a pivotal role in astrophysics and cosmology.

They are categorised into Type Ia, Ib, and Ic, with Type

Ia supernovae arising from the thermonuclear explosion

of white dwarfs in binary systems (either through single-

degenerate or double-degenerate scenarios) and serving

as critical ”standard candles” for measuring cosmic

distances due to their consistent peak luminosity. Their

light curves, powered by radioactive decay of nickel and

iron, enabled the discovery of the universe’s accelerating

expansion, attributed to dark energy. In contrast,

Type Ib/Ic supernovae result from the core collapse of

massive, stripped-envelope stars (like Wolf-Rayet stars)

and exhibit more diverse light curves. Despite their

signiﬁcance, key questions remain about progenitor

systems, metallicity eﬀects, and explosion mechanisms,

with ongoing research leveraging advanced surveys and

simulations. These cosmic explosions not only enrich

the interstellar medium with heavy elements but also

provide profound insights into stellar evolution and the

large-scale structure of the universe.

Geetha Paul’s article ”Beyond Morphology:

How Molecular Taxonomy is Reshaping Species

Identiﬁcation” explains that Molecular taxonomy has

revolutionised biological classiﬁcation by shifting

from traditional morphological approaches to genetic

analysis, overcoming limitations like phenotypic

plasticity and cryptic species. Techniques such as DNA

barcoding (e.g., CO1 for animals) and high-throughput

sequencing have uncovered hidden biodiversity,

revealing that many morphologically similar organisms

are genetically distinct species—examples include

Caribbean frogs splitting into 12 species and African

elephants reclassiﬁed into two separate species.

This paradigm shift has profound implications: it

resolves taxonomic conﬂicts, detects hybridisation (e.g.,

wolf-coyote hybrids), and aids conservation eﬀorts

by identifying evolutionarily signiﬁcant units and

combating wildlife traﬃcking through genetic forensics.

In microbiology, it has exposed vast uncultured diversity,

expanding known bacterial phyla from 12 to over 100.

Despite challenges like cost and data interpretation,

innovations like portable sequencers and AI promise

to democratise the ﬁeld. Molecular taxonomy not

only reﬁnes our understanding of life’s diversity but

also bridges gaps between species discovery and

conservation, proving indispensable in modern biology.

The article Ajay Vibhute, ”Classifying Parallelism:

Part-2” explores ﬁne-grained parallelism techniques that

optimise processor performance at the hardware level,

focusing on bit-level, instruction-level (ILP), and thread-

level parallelism (TLP). Bit-level parallelism enhances

processing eﬃciency by operating on multiple bits

simultaneously, particularly beneﬁting cryptography

and data compression through wider registers (e.g.,

64-bit) and SIMD units. ILP boosts throughput by

executing multiple instructions per cycle via pipelining

and out-of-order execution, though it faces limitations

from instruction dependencies and branch hazards. TLP

leverages multi-core architectures to run concurrent

threads, improving performance in parallel workloads

but requiring careful synchronisation to avoid race

conditions. While each technique oﬀers unique

advantages—bit-level for low-level operations, ILP

for single-core optimisation, and TLP for multi-core

scaling—their combined use in modern processors

enables eﬃcient handling of diverse computational

tasks, from high-performance computing to real-time

systems. Understanding these layers of parallelism

is crucial for designing hardware and software that

maximises computational eﬃciency.

iii

Figure 1: Sheelu Abrham and Arun Kumar Aniyan, visited airis4D.

Figure 2: As usual, research was the major subject of the discussions.

News Desk

Contents

Editorial ii

I Astronomy and Astrophysics 1

1 Black Hole Stories-18:

Gravitational Waves from The Binary Radio Pulsar 1913+16 2

1.1 The Nature of the Binary Pulsar PSR1913+16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.2 Detailed Observational Studies of the Binary Pulsar . . . . . . . . . . . . . . . . . . . . . . . . . 2

2 A Brief Introduction to PLASMA PHYSICS 6

2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.2 Particle Interaction and Collective Behaviour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.3 Criteria for Plasma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.4 Plasma in Nature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.5 Basic Plasma Phenomena . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.6 Applications of Plasma Physics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3 X-ray Astronomy: Through Missions 13

3.1 Satellites in 2000s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.2 SUZAKU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.3 AGILE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3.4 MAXI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3.5 Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

4 The Hunt for the Cosmic Radio Lines of Neutral Hydrogen 17

4.1 The Bold Prediction (Amidst Darkness) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

4.2 Independent Conﬁrmation and Other Ideas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

4.3 The Breakthrough Discovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

4.4 The Power of the 21 cm Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

4.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

5 Type I Supernovae: Stellar Explosions Without Hydrogen 21

5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

5.2 Classiﬁcation and Spectral Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

5.3 Progenitors and Explosion Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

5.4 Light Curves and Observational Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

5.5 Cosmological Signiﬁcance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

5.6 Current Research and Open Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

5.7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

CONTENTS

II Biosciences 24

1 Beyond Morphology: How Molecular Taxonomy is Reshaping Species Identiﬁcation 25

1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

1.2 Key Applications of Molecular Taxonomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

1.3 Challenges and Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

1.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

III Computer Programming 29

1 Classifying Parallelism: Part-2 30

1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

1.2 Bit-Level Parallelism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

1.3 Instruction-Level Parallelism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

1.4 Thread-Level Parallelism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

1.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Part I

Astronomy and Astrophysics

Black Hole Stories-18:

Gravitational Waves from The Binary Radio

Pulsar 1913+16

by Ajit Kembhavi

airis4D, Vol.3, No.5, 2025

www.airis4d.com

In this story we will consider detailed observations

of the binary radio pulsar 1913+16 and how these led

to ﬁrm evidence that gravitational waves exist.

1.1 The Nature of the Binary Pulsar

PSR1913+16

We have seen in the previous story that the binary

pulsar consists of two neutron stars each of which has a

mass of about 1.4 times the mass of the Sun, and radius

of about 10 km. Because of the second explosion, the

binary has a very eccentric orbit, so each neutron star

moves around the companion neutron star along a path

which is a narrow ellipse, as shown in Figure 2 of BHS-

17. The minimum distance between the two neutron

stars, which is known as the perihelion distance, is very

much smaller than the maximum distance between them.

Such a small minimum distance is possible only because

both neutron stars have a small radius, which permits

them to approach each other very closely. Normal stars,

because of their much larger radius, would not be able

to get so close without colliding and possibly getting

destroyed.

The compact nature of the neutron star binary

means that the gravitational force between them is very

strong, particularly at the perihelion distance, and the

neutron stars move with very high velocity along their

orbital paths. Newton’s theory of gravity cannot be

applied to such a system and we instead need to use

Einstein’s general theory of relativity. There are three

classical tests of general relativity which were mention

by Albert Einstein in the formulation of his theory of

gravitation: the existence of gravitational redshift, the

bending of light due to the eﬀects of a gravitational

ﬁled, and the precession of the perihelion of Mercury.

All these tests as well in phenomena like gravitational

lensing, only weak gravitational ﬁelds are involved, and

it could be argued that general relativity has been tested

only for such weak ﬁelds. The binary pulsar provided

the ﬁrst opportunity to test general relativity in a strong

gravitational ﬁeld regime.

1.2 Detailed Observational Studies of

the Binary Pulsar

The early observations by Hulse and Taylor

established that B1913+16 was a binary consisting

of a rapidly rotating radio pulsar and a companion.

The nature of the companion was not known, but it

was clear that it should be a compact object with a

small radius. If it were an extended object like a star

with a large radius, then as the pulsar went round it,

the pulsar would be eclipsed and pulses would not be

observed for the duration of the eclipse, but this was not

observed. The compact object could be a helium star,

white dwarf, neutron star or black hole. Observations

1.2 Detailed Observational Studies of the Binary Pulsar

and theoretical work over the years established that the

companion is a neutron star, rather than any of the other

possibilities. No radio pulses have been observed from

the companion. Therefore either (1) the companion is a

radio pulsar, but the radio beam from the companion

does not sweep past the Earth, so no pulsations are seen

or (2) it is not a pulsar. The fact that both components

of the binary are so compact is important in the analysis

of the system. If the companion had been an extended

object, the gravitational ﬁeld of the pulsar would have

distorted the shape of companion, and it would have

been diﬃcult to interpret the observations. The neutron

stars in the binary do not have such distortions, and

being compact, can approach each other very closely.

The system therefore is an ideal laboratory for the study

of gravitational eﬀects.

Hulse and Taylor and later Taylor and J. Weisberg

continued to study B1913+16 for many years with the

Arecibo radio telescope. A pulse is detected every

time the radio beam from the pulsar sweeps across the

telescope. The time between successive pulses is equal

to the rotation period of the pulsar, which is very close

to 59 milliseconds (ms). The rotation period remains

very nearly constant over long periods of time, because

the neutron star is such a massive object and it is very

diﬃcult to aﬀect its rotation. The rotation of the pulsar

does slow down measurably over long periods of time,

since the pulsar loses energy because of the radiation

that it emits.

Even though the pulsar rotation period changes

very slowly, the time between successive pulses received

on the Earth can change due to various other reasons. As

the pulsar moves along its orbit around the companion

star, it is sometimes moving towards the Earth, and at

other times it is moving away. During its motion towards

the Earth, the observed time between two successive

pulses decreases and becomes less than then the rotation

period of the pulsar. When the pulsar is moving away,

the observed time between the pulses increases and

becomes greater than the rotation period. This is known

as the Doppler eﬀect. Using sophisticated instruments

and measurement techniques, Taylor and Weisberg were

able to measure the arrival time of successive pulses

extremely accurately. This in turn led to very accurate

Figure 1: The change in the velocity of the pulsar as

it moves along an orbit. The x-axis shows the position

along an orbit and the y-axis the velocity of the pulsar

in the direction of the Earth. When the velocity is

positive the pulsar is moving away from the Earth while

negative velocity indicates that the pulsar is approaching

the Earth.

Image Credit: R. A. Hulse and J. H. Taylor, Astrophysical Journal 195, L51, 1975.

velocity measurements. Such measurements, made over

many orbits are shown in Figure 1. It is the existence

of such variation that establishes the binary nature of

the object.

From arrival time measurements it is possible to

infer many details about the orbit, including the size and

shape of the orbit, how closely the pulsar approaches its

companion and so forth. Such calculations have been

done over the years for several binary star systems having

components as ordinary stars using Newton’s theory

of gravitation. What is generally not possible in such

calculations is the measurement of the masses of the

stars in the binary. The masses can be estimated only in

special circumstances and accurate values can seldom be

obtained. The situation is quite diﬀerent for B1913+16.

Here the gravitational ﬁeld is very strong, and general

relativistic eﬀects, including gravitational redshift, and

the precession of the perihelion, which we discussed

in earlier stories, are present. These lead to further

changes in the pulse arrival times. When calculations

are performed to account for all the eﬀects, using general

relativity, it turns out that all the parameters which are

required to determine the shape of the orbit, as well as

the mass of the pulsar and its companion can be very

accurately determined.

1.2 Detailed Observational Studies of the Binary Pulsar

The values for some important quantities

calculated from the analysis of pulse arrival times are

shown in Table 1. These are based on measurements

made for more than thirty years after the discovery of

the pulsar.

Table 1.1: Pulsar System Parameters

Parameter Value

Pulsar Rotation Period 59.0300032180 ms

Orbital period 7.7519938773864 hours

Maximum Separation 3,153,600 km

Minimum Separation 746,600 km

Precession of Perihelion 4.226598 degrees/year

Pulsar Mass 1.4398 Solar Mass

Companion Mass 1.3886 Solar Mass

The many places after the decimal point show

how accurate the measurements are. The precession

of the perihelion in the system is about 4.2 degrees

per year. This is about 35,000 times the value for the

precession of Mercury, which is only 43 arcseconds

per century! This shows how strong the gravitational

ﬁeld experienced by the pulsar is, because of itsof close

approach to the companion. The mass of the pulsar

and the companion neutron star are 1.44 and 1.39 times

the mass of the Sun respectively. When such mass

measurements were ﬁrst reported some years after the

discovery of the binary pulsar, they represented the ﬁrst

ever direct measurements of neutron star mass. The

measurements are also the most accurately measured

stellar mass ever made. The fact that the two masses are

so close to the Chandrasekhar limit of about 1.4 times

the Solar mass has implications for the way in which

the neutron stars were formed.

The maximum distance between the pulsar and

its companion is about 3.15 million km, which is very

much smaller than the Earth-Sun distance of 150 million

km. The minimum or perihelion distance between the

two is 746,600 km, which is comparable to the radius

of the Sun, which is 700,000 km. The two components

of the binary can approach each other so closely only

because they are very compact objects. If the companion

were more extended, like a normal star, it would be

disrupted if the distance of approach was so small. At

the perihelion, the pulsar moves with a velocity of about

400 km/sec. The time taken to complete one orbit,

which is known as the orbital period, is about 7 hours

and 45 minutes. The binary system is at a distance of

21,000 light years away from us. Because of its position

in the sky, the system will be visible only between 1941

and 2025. It was indeed fortunate that Hulse and Taylor

could detect the system during this limited interval of

time that is available for its observation from the Earth.

Soon after the discovery of the binary pulsar, it

was pointed out by Robert Wagoner that the observation

of change in the binary rotation period with time will

allow us to test the presence of gravitational waves. The

binary pulsar is very compact and the gravitational force

between the two neutron stars is very strong. The orbit

of the pulsar around the companion is highly elliptical

in nature. Such a binary emits a signiﬁcant amount of

gravitational waves due to the high acceleration. The

emission results in the loss energy by the binary, and

consequently the binary shrinks in size. The two neutron

stars gradually come closer together and therefore

revolve faster around each other, leading to a decrease

in the orbital period of the binary. A measurement

of the change in their period of revolution allows a

measurement of the rate at which they are losing energy

through the emission of gravitational waves. This can

be compared with the value predicted by Einstein’s

theory. If the expected and observed values happen

to be equal, it would provide a direct validation of the

existence and emission of gravitational waves.

Hulse and Taylor continued their work on the

observations of the binary pulsar system and in 1978,

four years after its discovery, announced that they had

indeed found a decrease of the binary period which

was consistent with the prediction by Einstein’s theory.

The general relativistic value was obtained using the

measured parameters of the binary pulsar. This was

the ﬁrst time that the emission of gravitational waves

predicted in 1916 was seen to really exist. Observations

accumulated over the years and reported in 2010 have

shown that the observed rate of change of orbital period

and the prediction of Einstein’s theory agree to better

than one percent. The change in orbital period changes

the time taken by the pulsar to pass the perihelion in

successive orbits. Because the orbit shrinks in size,

the perihelion passage occurs somewhat earlier for

1.2 Detailed Observational Studies of the Binary Pulsar

Figure 2: The change in rotation period of the binary

B1913+16 over a span of 30 years from 1975 to 2005 as

predicted by Einstein’s General theory of relativity and

as observed. The x-axis shows the time of observation

and the y-axis provides a measure of the decrease in

time taken for successive revolutions (see the text below

for some detail), which indicates shrinking of the orbit.

The dots show the observed values. The agreement

between observed and predicted values is remarkable

and proves the existence of gravitational waves. If

gravitational waves were not being emitted, the graph

would have been a horizontal straight line as shown at

the top.

Image Credit: J. M. Weisberg, D. J. Nice and J. H. Taylor, Astrophysical Journal 722, 1030, 2010.

successive orbits. The cumulative shift over many years

of observation is shown in Figure 2. The continuous

curve shows the cumulative shift with time as predicted

by Einstein’s theory, while the dots are the observed

values. The dots fall very closely on the predicted line,

with any observed departure from the line being too

small (smaller than 1 percent ) to be seen. The emission

of gravitational waves is therefore very well validated,

though gravitational waves are not directly detected

through these observations.

Hulse and Taylor were given the Nobel prize in

physics for 1993. The Nobel citation said that the

award was for their discovery of a new type of pulsar, a

discovery that has opened up new possibilities for the

study of gravitation.

Next Story: In the next story we will describe the

Advance LIGO gravitational wave detectors.

About the Author

Professor Ajit Kembhavi is an emeritus

Professor at Inter University Centre for Astronomy

and Astrophysics and is also the Principal Investigator

of the Pune Knowledge Cluster. He was the former

director of Inter University Centre for Astronomy and

Astrophysics (IUCAA), Pune, and the International

Astronomical Union vice president. In collaboration

with IUCAA, he pioneered astronomy outreach

activities from the late 80s to promote astronomy

research in Indian universities.

A Brief Introduction to PLASMA PHYSICS

by Abhishek P S

airis4D, Vol.3, No.5, 2025

www.airis4d.com

2.1 Introduction

What is Plasma?

Radiant matter, that is what Sir William Crookes

mentioned the new state of matter he observed in his

laboratory. Matter exists in the form of ionized gas in

this radiant matter. Strange behaviour of the constituent

particles such as electrons and nucleus made this new

state of matter unique and captivated among the science

community. Analogy of these particles with the blood

plasma inspirited Irving Langmuir to name this radiant

matter as Plasma [1]. The word Plasma comes from

the Greek and means ”something molded”.

From a scientiﬁc point of view, matter in the known

universe is often classiﬁed in terms of four states: solid,

liquid, gaseous, and plasma. The word plasma is

used to describe a wide variety of macroscopically

neutral substances containing many interacting free

electrons and ionized atoms or molecules, which exhibit

collective behaviour due to the long-range coulomb

forces. Not all media containing charged particles,

however, can be classiﬁed as plasmas. For a collection

of interacting charged and neutral particles to exhibit

plasma behaviour it must satisfy certain conditions, or

criteria, for plasma existence.

A given substance is found in one of these states

depends on the random kinetic energy (thermal energy)

of its atoms or molecules i.e, on its temperature.The

equilibrium between these particle thermal energy and

the inter-particle binding forces determines the state.

By heating a solid or liquid substance, the atoms or

molecules acquire more thermal kinetic energy until

they are able to overcome the binding potential energy.

This leads to phase transitions, which occur at constant

temperature for a given pressure. The amount of energy

required for the phase transition is called the ”latent

heat”. If suﬃcient energy is provided, a molecular gas

will gradually dissociate into an atomic gas as a result

of collisions between those particles whose thermal

kinetic energy exceeds the molecular binding energy.

At suﬃciently elevated temperatures an increasing

fraction of the atoms will possess enough kinetic energy

to overcome,by collisions, the binding energy of the

outermost orbital electrons, and an ionized gas or plasma

results. However, this transition from a gas to a plasma

is not a phase transition in the thermodynamic sense,

since it occurs gradually with increase in temperature.

2.2

Particle Interaction and Collective

Behaviour

The properties of a plasma are markedly dependent

upon the particle interactions. One of the basic features

that distinguish the behaviour of plasma from that of

ordinary ﬂuids and solids is the existence of collective

eﬀects. Due to the long range of electromagnetic

forces, each charged particle in the plasma interacts

simultaneously with a considerable number of other

charged particles, resulting in important collective

eﬀects that are responsible for the wealth of physical

phenomenon that takes place in plasma. In a plasma

we must distinguish between charge-charge and charge-

neutral interactions. A charged particle is surrounded

by an electric ﬁeld and interacts with the other charged

particles according to the coulombs force law, with its

dependence on the inverse of the square of the separation

2.3 Criteria for Plasma

distance. Further more, a magnetic ﬁeld is associated

with a moving charged particle, which also produces a

force on other moving charges.The charged and neutral

particles interact through electric polarization ﬁelds

produced by distortion of the neutral particle’s electronic

cloud during a close passage of the charged particle.The

ﬁeld associated with neutral particles involves short-

range forces, such that their interaction is eﬀective

only for inter-atomic distance suﬃciently small to

perturb the orbital electrons. It is appreciable when

the distance between the centres of the interacting

particles is of the order of their diameter, but nearly

zero when they are farther apart. It’s characteristics can

be adequately described only by quantum-mechanical

considerations.In many cases this interaction involves

permanent or induced electric dipole moments. A

distinction can be made between weakly ionized and

strongly ionized plasmas in terms of the nature of the

particle interactions. In a weakly ionized plasma the

charge-neutral interactions dominate over the multiple

coulomb interactions. When the degree of ionization

is such that the multiple coulomb interactions become

dominant,the plasma is considered strongly ionized.

As the degree of ionization increases,the coulomb

interactions become increasingly important so that in a

fully ionized plasma all particles are subjected to the

multiple coulomb interactions.

2.3 Criteria for Plasma

2.3.1 Debye Shielding

A fundamental characteristic of the behaviour of a

plasma is its ability to shield out electric potentials that

are applied to it. Suppose we tried to put an electric

ﬁeld inside a plasma by inserting two charged balls

connected to a battery (Fig. 1). The balls would attract

particles of the opposite charge, and almost immediately

a cloud of ions would surround the negative ball and

a cloud of electrons would surround the positive ball.

(We assume that a layer of dielectric keeps the plasma

from actually recombining on the surface, or that the

battery is large enough to maintain the potential in spite

of this.) If the plasma were cold and there were no

Figure 1: The Debye length

is an important physical

parameter for the description of plasma. It provides

a measure of the distance over which the inﬂuence of

the electric ﬁeld of an individual charged particle is

felt by the other charged particles inside the plasma.

The charged particles arrange themselves in such a way

as to eﬀectively shield any electrostatic ﬁelds within a

distance if the order of the Debye length.This shielding

of electrostatic ﬁelds is a consequence of the collective

eﬀects of the plasma particles. A calculation of the

shielding distance was ﬁrst performed by Debye ,for an

electrolyte.

Image courtesy: https://www.kindpng.com/imgv/Twwhoib show- more-plots-debye-shielding-in-p

lasma-phy

thermal motions, there would be just as many charges in

the cloud as in the ball; the shielding would be perfect,

and no electric ﬁeld would be present in the body of

the plasma outside of the clouds. On the other hand, if

the temperature is ﬁnite, those particles that are at the

edge of the cloud, where the electric ﬁeld is weak, have

enough thermal energy to escape from the electrostatic

potential well. The ”edge” of the cloud then occurs at

the radius where the potential energy is approximately

equal to the thermal energy KBT of the particles, and

the shielding is not complete. Potentials of the order of

KBT/e can leak into the plasma and cause ﬁnite electric

ﬁelds to exist there[2].

When the boundary surface is introduced in a

plasma, the perturbation produced extends only upto

a distance of the order of

from the surface. In the

neighbourhood of any surface inside the plasma there

is a layer of width of the order of

known as Plasma

Sheath, inside which the condition of macroscopic

electrical neutrality may not be satisﬁed. Beyond

the plasma sheath region there is the plasma region

,where macroscopic neutrality is maintained[3]. The

2.4 Plasma in Nature

Debye shielding eﬀect is a characteristic of all plasmas

,although it does not occur in every medium that

contains charged particles. A necessary and obvious

requirement for the existence of a plasma is that the

physical dimensions of the system be large compared

. Otherwise there is just not suﬃcient space for

the collective shielding eﬀect to take place ,and the

collection of charged particles will not exhibit plasma

behaviour. If L is a characteristic dimension of plasma

,a ﬁrst criteria for the deﬁnition of plasma is therefore

L >> λ

2.3.2 Quasineutrality

In the absence of external disturbances a plasma

is macroscopically neutral. This means that under

equilibrium conditions with no external forces present,

in a volume of the plasma suﬃciently large to contain

a large number of particles and yet suﬃciently small

compared to the characteristic lengths for variation

of macroscopic parameters such as density and

temperature, the net resulting electric charge is zero. In

the interior of the plasma the microscopic space charge

ﬁelds cancel each other and no net space charge exists

over a macroscopic region[4]. If this macroscopic

neutrality was not maintained, the potential energy

associated with the resulting coulomb forces could

be enormous compared to the thermal particle kinetic

energy. Therefore, a plasma temperature of several

millions of degrees Kelvin would be required to balance

the electric potential energy with the average thermal

particle energy. Departures from macroscopic electrical

neutrality can naturally occur only over distances in

which a balance is obtained between the thermal particle

energy, which tends to disturb the electrical neutrality,

and the electrostatic potential energy resulting from any

charge separation, which tends to restore the electrical

neutrality. This distance is of the order of a characteristic

length parameter of the plasma, called the Debye length.

In the absence of external forces, the plasma cannot

support departures from macroscopic neutrality over

larger distances than this, since the charged particles are

able to move freely to neutralize any regions of excess

space charge in response to the large coulomb forces

that appear.

2.3.3 Plasma Frequency

An important plasma property is the stability of its

macroscopic space charge neutrality. When a plasma

is instantaneously disturbed from the equilibrium

condition, the resulting internal space charge ﬁelds

give rise to collective particle motions that tend to

restore the original charge neutrality. These collective

motions are characterised by a natural frequency of

oscillation known as the Plasma frequency. Since these

collective oscillations are high frequency oscillations,

the ions, because of their heavy mass,a re to a certain

extend unable to follow the motion of the electrons.The

electrons oscillate collectively about the heavy ions,the

necessary collective restoring force being provided

by the ion-electron coulomb attraction.The period of

this natural oscillation constitutes a meaningful time

scale against which can be compared the dissipative

mechanisms tending to destroy the collective electron

motions.

Consider a plasma initially uniform and at

rest,and suppose that by some external means a small

charge separation is produced inside it. When the

external disturbing force is removed instantaneously, the

internal electric ﬁeld resulting from charge separation

collectively accelerates the electrons in an attempt to

restore the charge neutrality. However, because of

their inertia, the electrons move beyond the equilibrium

position, and an electric ﬁeld is produced in the opposite

direction. This sequence of movements repeats itself

periodically, with a continuous transformation of kinetic

energy into potential energy, and vice versa, resulting

in fast collective oscillations of the electrons about

the more massive ions. On the average the plasma

maintains its macroscopic charge neutrality.

2.4 Plasma in Nature

2.4.1 Sun and its Atmosphere

The sun, which is our nearest star and upon which

the existence of life on Earth fundamentally depends, is

a plasma phenomenon[5]. Its energy output is derived

2.4 Plasma in Nature

from thermonuclear fusion reactions of protons forming

helium ions deep in its interior, where temperatures

exceed

1.2 × 10

K. The high temperature of its interior

and the consequent thermonuclear reactions keep the

entire sun gaseous. Due to its large mass (

2 × 10

kg),

the sun’s gravitational force is suﬃcient to prevent the

escape of all but the most energetic particles and, of

course, radiation from the hot solar plasma. There is

no sharp boundary surface to the sun. Its visible part

is known as the solar atmosphere, which is divided

into three general regions or layers. The photosphere,

with a temperature of about 6,000 K, comprises the

visible disk, the layer in which the gases become opaque,

and is a few hundred kilometres thick. Surrounding

the photosphere there is a reddish ring called the

chromosphere, approximately 10,000 km thick, above

which ﬂame-like prominences rise with temperatures of

the order of 100,000 K. Surrounding the chromosphere

there is a tenuous hot plasma, extending millions of

kilometres into space, known as the corona. A steep

temperature gradient extends from the chromosphere to

the hotter corona, where the temperature exceeds

K. .

2.4.2 Solar Wind

A highly conducting tenuous plasma called the

solar wind, composed mainly of protons and electrons,

is continuously emitted by the sun at very high speeds

into interplanetary space, as a result of the supersonic

expansion of the hot solar corona. The solar magnetic

ﬁeld tends to remain frozen in the streaming plasma due

to its very high conductivity. Because of solar rotation,

the ﬁeld lines are carried into Archimedean spirals by

the radial motion of the solar wind[6].

2.4.3 Magnetosphere and Van Allen Belts

As highly conducting solar wind impinges on

the Earth’s magnetic ﬁeld, it compresses the ﬁeld on

the sunward side and ﬂows around it at supersonic

speeds. This creates a boundary,called the magneto-

pause, which is roughly spherical on the sunward side

and roughly cylindrical in the anti-sun direction (Fig.

2). The inner region, from which the solar wind is

Figure 2: Formation of Magneto-pause

Image courtesy: https://en.wikipedia.org/wiki/Magnetopause

excluded and which contains the compressed Earth’s

magnetic ﬁeld, is called the magnetosphere. Inside

the magnetosphere we ﬁnd the Van Allen radiation

belts, in which energetic charged particles (mainly

electrons and protons) are trapped into regions where

they execute complicated trajectories that spiral along

the geomagnetic ﬁeld lines and, at the same time, drift

slowly around the Earth[7]. The origin of the inner

belt is ascribed to cosmic rays, which penetrate into the

atmosphere and form proton-electron pairs that are then

trapped by the Earth’s magnetic ﬁeld. The outer belt is

considered to be due to and maintained by streams of

plasma consisting mainly of protons and electrons that

are ejected from time to time by the sun. Depending

on solar activity, particularly violent solar eruptions

may occur with the projection of hot streams of plasma

material into space. The separation into inner and

outer belts reﬂects only an altitude-dependent energy

spectrum, rather than two separate trapping regions.

2.4.4 Ionosphere

The large natural blanket of plasma in the

atmosphere, which envelopes the Earth from an altitude

of approximately 60 km to several thousands of

kilometres, is called the ionosphere. The ionized

particles in the ionosphere are produced during the

daytime through absorption of solar extreme ultraviolet

2.5 Basic Plasma Phenomena

and X-ray radiation by the atmospheric species. As

the ionizing radiation from the sun penetrates deeper

and deeper into the Earth’s atmosphere, it encounters

a larger and larger density of gas particles, producing

more and more electrons per unit volume. However,

since radiation is absorbed in this process, there

is a height where the rate of electron production

reaches a maximum. Below this height the rate of

electron production decreases, in spite of the increase in

atmospheric density, since most of the ionizing radiation

was already absorbed at the higher altitudes

2.4.5 Plasmas Beyond the Solar System

Beyond the solar system we ﬁnd a great variety

of natural plasmas in stars, interstellar space, galaxies,

intergalactic space, and far beyond to systems quite

unknown before the start of astronomy from space

vehicles. There we ﬁnd a variety of phenomena of great

cosmological and astrophysical signiﬁcance, including

interstellar shock waves from remote supernova

explosions, rapid variations of X-ray ﬂuxes from neutron

stars with densities like that of atomic nuclei, pulsating

radio stars or pulsars (which are theoretically pictured

as rapidly rotating neutron stars with plasmas emitting

synchrotron radiation from the surface), and the plasma

phenomena around the remarkable black holes (which

are considered to be singular regions of space into

which matter has collapsed, possessing such a powerful

gravitational ﬁeld that nothing, whether material objects

or even light itself, can escape from them).

2.5 Basic Plasma Phenomena

The fact that some or all of the particles in a

plasma are electrically charged and therefore capable

of interacting with electromagnetic ﬁelds, as well as of

creating them, gives rise to many novel phenomena that

are not present in ordinary ﬂuids and solids.Because

of high electron mobility, plasmas are generally very

good electrical conductors, as well as good thermal

conductors. The presence of density gradients in

a plasma causes the particles to diﬀuse from dense

regions to regions of lower density. Due to their lower

mass, electrons tend to diﬀuse faster than the ions

, generating a polarization electric ﬁeld as a result

of charge separation. An important characteristic of

plasma is their ability to sustain a great variety of

wave phenomena.e.g electrostatic plasma wave and

electromagnetic wave. The study of waves in plasma

provides signiﬁcant information on plasma properties

and is very useful for plasma diagnostics. Dissipative

processes, such as collisions ,produce damping of

wave amplitude. Another important aspect of plasma

behaviour is the emission of radiation.The main interest

in plasma radiation lies in the fact that it can be used to

infer plasma properties. Radiation can be from emitting

atoms or molecules, and also from accelerated charges.

At the same time, recombination of ions and electrons

to form neutral particles also occur. Another important

aspect of plasma behaviour is the emission of radiation.

The main interest in plasma radiation lies in the fact

that it can be used to infer plasma properties. Radiation

can be from emitting atoms or molecules, and also from

accelerated charges. At the same time, recombination of

ions and electrons to form neutral particles also occur.

2.6 Applications of Plasma Physics

Plasmas can be characterized by the two

parameters n and KBTe. Plasma applications cover

an extremely wide range of n and

; n varies

over 28 orders of magnitude from

−3

, and

can vary over seven orders from 0.1 to

eV. Some of these applications are discussed very

brieﬂy below. The tremendous range of density can

be appreciated when one realizes that air and water

diﬀer in density by only

, while water and white

dwarf stars are separated by only a factor of

. Even

neutron stars are only

times denser than water. Yet

gaseous plasmas in the entire density range of

can

be described by the same set of equations, since only

the classical (non-quantum mechanical) laws of physics

are needed[8].

2.6 Applications of Plasma Physics

Figure 3: Magnetohydrodynamic converter

Image courtesy: https://en.wikipedia.org/wiki/Magnetohydrodynamic converter

2.6.1 Gas Discharges

The earliest work with plasmas was that of

Langmuir, Tonks, and their collaborators in the 1920’s.

This research was inspired by the need to develop

vacuum tubes that could carry large currents, and

therefore had to be ﬁlled with ionized gases. The

research was done with weakly ionized glow discharges

and positive columns typically with

2 eV and

< 10

−3

. It was here that the shielding

phenomenon was discovered: the sheath surrounding

an electrode could be seen visually as a dark layer.

Gas discharges arc encountered nowadays in mercury

rectiﬁers, hydrogen thyratrons, ignitrons. spark gaps,

welding arcs, neon and ﬂuorescent lights, and lightning

discharges.

2.6.2 MHD Energy Conversion and ION

Propulsion

Getting back down to earth, we come

to two practical applications of plasma physics.

Magnetohydrodynamic (MHD) energy conversion

utilizes a dense plasma jet propelled across a magnetic

ﬁeld to generate electricity (Fig. 3). The Lorentz force

q(v x B), where v is the jet velocity, causes the ions

to drift upward and the electrons downward, charging

the two electrodes to diﬀerent potentials. Electrical

current can then be drawn from the electrodes without

the ineﬃciency of a heat cycle[2].

The same principle in reverse has been used to

develop engines for interplanetary missions. In Plasma

jet, a current is driven through a plasma by applying a

voltage to the two electrodes. The j x B force shoots

the plasma out of the rocket, and the ensuing reaction

force accelerates the rocket. The plasma ejected must

always be neutral; otherwise, the space ship will charge

to a high potential.

2.6.3 Space Physics

Another important application of plasma physics

is in the study of the earth’s environment in space. A

continuous stream of charged particles, called the solar

wind, impinges on the earth’s magnetosphere, which

shields us from this radiation and is distorted by it

in the process. Typical parameters in the solar wind

are n =

5 × 10

−3

= 10

eV,

= 50

eV,

B =

5 × 10

−9

T, and drift velocity 300 km/sec. The

ionosphere, extending from an altitude of 50 km to 10

earth radii, is populated by a weakly ionized plasma

with density varying with altitude up to n =

−3

. The temperature is only

−1

eV. The Van Allen

belts are composed of charged particles trapped by the

earth’s magnetic ﬁeld. Here we have

n <= 10

−3

<= 1keV

1eV

, and B =

500 × 10

−9

. In

addition, there is a hot component with n =

−3

and K

= 40keV [2].

2.6.4 Controlled Thermonuclear Fusion

The most important application of man-made

plasmas is in the control of thermonuclear fusion

reactions, which holds a vast potential for the generation

of power[9]. Nuclear fusion is the process whereby two

light nuclei combine to form a heavier one, the total

ﬁnal mass being slightly less than the total initial mass.

The mass diﬀerence

appears as energy (E) according

to Einstein’s famous law E =

∆mc

where c denotes

the speed of light. The nuclear fusion reaction is the

source of energy in the stars, including the sun. The

conﬁnement of the hot plasma in this case is provided

by the self-gravity of the stars.

The basic problem in achieving controlled fusion

is to generate a plasma at very high temperatures (with

thermal energies at least in the 10 ke V range) and

hold its particles together long enough for a substantial

number of fusion reactions to take place. The need for

high temperatures comes from the fact that, in order

to undergo fusion, the positively charged nuclei must

come very close together (within a distance of the order

−14

m, which requires suﬃcient kinetic energy to

overcome the electrostatic coulomb repulsion.

2.6 Applications of Plasma Physics

2.6.5 Other Plasma Devices

The thermionic energy converter is a device that

utilizes a caesium plasma between two electrodes to

convert thermal energy into electrical energy. The

cathode is heated, so that electrons are emitted from

the surface, and the anode is cooled. Due to the

presence of the caesium plasma, very large electrical

currents can be produced at the expense of a signiﬁcant

fraction of the thermal energy applied to the cathode[8].

Examples of applications involving gas discharges

include the ordinary ﬂuorescent tubes and neon lights

used for illumination and for signs, mercury rectiﬁers,

spark gaps, a number of specialized tubes like the

hydrogen thyratrons and the ignitrons, which are

used for switching, and the arc discharges or plasma

jets, which are the source of temperatures two or

more times as high as the hottest gas ﬂames and

which are used in metallurgy for cutting, melting, and

welding metals. Two major applications in the area

of communications are the long distance radio wave

propagation by reﬂection in the ionospheric plasma and

the communication with a space vehicle through the

plasma layer that forms around it during the re-entry

period into the Earth’s atmosphere.

References

Lewi, Tonks.,The Birth of “Plasma”. Am. J.

Phys. 1 September 1967; 35 (9): 857–858.

https://doi.org/10.1119/1.1974266

Francis, F, Chen., (2015). Introduction to

Plasma Physics and Controlled Fusion (3rd ed.).

Springer Cham. https://doi.org/10.1007/978-3-

319-22309-4

Hull AW., Langmuir I., Control of an Arc

Discharge by Means of Grid. Proc Natl Acad Sci

USA. 1929 March 15;15(3): 218-225

Rozhansky, V., (2023). Quasineutral Plasma

and Sheath Structure. In: Plasma Theory.

Springer, Cham. https://doi.org/10.1007/978-

3-031-44486-9 3

Simon, F, Green., Mark, H, Jones., S, Jocelyn,

Burnell., An Introduction to the Sun and Stars

2004, Cambridge University Press

Schrijver, Carolus, J.; Zwaan, Cornelis., (2000).

Solar and stellar magnetic activity. Cambridge

University Press. ISBN 978-0-521-58286-5.

Li, W.; Hudson, M.K. (2019). Earth’s Van Allen

Radiation Belts: From Discovery to the Van

Allen Probes Era. J. Geophys. Res. 124 (11):

8319–8351

Goldston, R,J., (1995). Introduction to

Plasma Physics (1st ed.). CRC Press.

https://doi.org/10.1201/9780367806958

Kenro, Miyamoto.,(2005) Plasma Physics and

Controlled Nuclear Fusion. Springer Berlin,

Heidelberg. https://doi.org/10.1007/3-540-

28097-9

About the Author

Abishek P S is a Research Scholar in

the Department of Physics, Bharata Mata College

(Autonomous) Thrikkakara, kochi. He pursues

research in the ﬁeld of Theoretical Plasma physics.

His works mainly focus on the Nonlinear Wave

Phenomenons in Space and Astrophysical Plasmas.

X-ray Astronomy: Through Missions

by Aromal P

airis4D, Vol.3, No.5, 2025

www.airis4d.com

3.1 Satellites in 2000s

In the previous article, we discussed the satellites

that were launched between 2000-2005. All these

satellites were not primarily dedicated to X-ray

astronomy. They carried X-ray instruments for follow-

up observations of high-energy phenomena like gamma-

ray bursts. In this article, we will discuss the satellites

launched in the second half of this decade. In this period,

missions primarily focused on X-rays that changed and

are still contributing to our understanding of high-energy

phenomena.

3.2 SUZAKU

Suzaku is the ﬁfth X-ray astronomy satellite by

the Japanese Aerospace Exploration Agency (JAXA),

built in collaboration with NASA. This mission is a

combined eﬀort of 21 universities from Japan and

three research organizations from the USA. Suzaku is

a red bird popularly found in Japanese and Chinese

mythologies. Suzaku satellite is also known as ASTRO-

EII. Suzaku was launched in July 2005 into a Low Earth

Orbit (LEO) of Perigee and Apogee of 550 km and

570 km, respectively. This orbit had an inclination of

○

providing an orbital period of 96 minutes. Suzaku

was launched as a complementary to Chandra and

XMM-Newton observatories, and it was operational till

September 2015. It had imaging capabilities in the lower

energy range of 0.2-12 keV and used a nested grazing

incident telescope called an X-ray Telescope(XRT) to

focus the incoming photons into the optical plane. There

are 5 XRT units known as XRTI0, XRTI1, XRTI2,

XRTI3 and XRTS. All ﬁve XRTs are placed in the

Extensible Optical Bench (EOB), and the scientiﬁc

instruments are placed in their focal plane. Suzaku

covered an energy range of 0.2 - 600 keV.

There were 3 scientiﬁc detectors in Suzaku:

X-ray Imaging Spectrometer (XIS) is an X-ray

sensitive silicon Charge Coupled Device(CCD)

that is similar to those used in ASCA SIS,

Chandra ACIS, and XMM-Newton EPIC.

XIS enables high-sensitivity imaging and

spectroscopy across the 0.2–12 keV energy band.

There are four identical sets of XISs situated in

the focal planes of the four XRT-Is. XIS has

a ﬁeld of view of

17.

′

8 × 17.

′

with an energy

resolution of 130 eV at 6 keV with an eﬀective

area of 400 cm

at 1.5 keV.

X-Ray Spectrometer (XRS) is the ﬁrst micro-

calorimeter used in an X-ray satellite. The XRS

utilized a 6×6 array of mercury telluride (HgTe)

micro-calorimeters with 30 active pixels. It uses

the temperature change to identify the energy of

the incident X-ray photons. It had a stunning

spectral resolution of 6-7 eV at 6 keV. The energy

bandwidth of XRS was the same as that of XIS.

It is positioned in the focal plane of XRT-S. After

the launch, its cryogenic system failed, so no

X-ray observation was performed. But it paved

the path to the upcoming missions.

Hard X-ray Detector (HXD) is a combination of

16 independent units arranged in a 4×4 grid of

the GSO well-type phoswich counters (

50 keV)

and the silicon PIN diodes (

50 keV). It covered

an energy range of 10-700 keV. HXD did not have

3.3 AGILE

Figure 1: Side view of Suzaku satellite.

Credits: MITSUDA et al. 2007

any imaging capabilities. It provided an eﬀective

area of 142

at 20 keV for PIN diodes and

273

at 150 keV GSO phoswich counters. It

also had a timing resolution of

61µs

in timing

mode.

Suzaku’s observations of the Perseus Galaxy

Cluster revealed a uniform distribution of iron across its

11-million-light-year expanse. Suzaku’s detection of

Chromium and Manganese in the Perseus Cluster’s

IGM - the ﬁrst such intergalactic measurements -

conﬁrmed that billions of type Ia supernovae contributed

to this metal enrichment. Suzaku’s high-resolution

spectroscopy enabled precise measurements of black

hole spin in AGN like MCG–6-30-15. Suzaku identiﬁed

AE Aquarii as a white dwarf emitting pulsed X-rays

akin to neutron star pulsars.

3.3 AGILE

The Astro-rivelatore Gamma a Immagini LEggero

(AGILE) is a Small Scientiﬁc Mission satellite,

developed and operated by the Italian Space Agency

(ASI). It is gamma-ray astronomy mission launched on

April 23, 2007 from Sriharikota, India. It is launched

into a LEO of perigee 509 km and apogee 533 km. The

satellite was operational until January 2024. It covered

an energy band of 8 keV to 50 GeV, from hard X-rays

to Gamma rays.

AGILE had 3 scientiﬁc instruments on board:

Gamma Ray Imager Detector (GRID) consists of

Figure 2: MAXI overview.

Credits: Mihara et al. 2022

a Silicon-Tungsten Tracker, a Cesium Iodide Mini-

Calorimeter (MC), an Anti-coincidence system

(AC) made of segmented plastic scintillators, and

a Data Handling system (DH). The GRID is

sensitive in the energy range 30MeV − 50GeV .

SuperAGILE (SA) consist of four units of

coded mask imaging system paired with silicon

microstrip detectors. SA is a hard X-ray

instrument that covers an energy range of 15-

45 keV. SA’s anti-coincidence system is shared

with AGILE’s Gamma Ray Imaging Detector

(GRID).

Mini-Calorimeter (MCAL) comprised 30 Cesium

Iodide Thallium-doped [CsI(Tl)] scintillator bars.

It detects gamma rays in the 300 keV–100 MeV

energy range.

3.4 MAXI

The Monitor of All-Sky X-ray Image, MAXI, is a

Japanese experiment onboard the International Space

Station. It is the ﬁrst experiment to be installed on

the Japanese Experiment Module Exposed Facility

(JEM-EF or Kibo-EF) on the ISS. It is also the ﬁrst

high-energy astrophysical experiment placed on the

space station. MAXI was launched by the space shuttle

STS-127 Endeavour in July 2009 and delivered to the

ISS. MAXI’s primary object is monitoring transient

events. It is a survey experiment that covered a large

fraction of the sky. After 15 years of service, it is still

providing valuable scientiﬁc outputs and discovering

new transient sources and its outbursts. MAXI performs

a complete sky survey every 96 minutes (orbital period

of ISS). MAXI covers an energy range of 0.5 keV - 30

keV.

MAXI has two scientiﬁc instruments:

3.5 Reference

Gas Slit Camera (GSC) employs slit camera

optics and has the advantage of being free from

source contamination than a coded mask. The

entire GSC system is composed of six identical

units, and it uses 12 large-area proportional

counters ﬁlled with Xe gas to detect X-rays. It

had a total area of 5350

and worked in the

energy range of 2-30 keV. This system covers a

wide rectangular FOV of 160

○

× 1.5

○

Solid-State Slit Camera (SSC) is a CCD camera

that works in 0.5–12 keV energy range. The SSC

is installed on the GSC and complements the GSC

by focusing on lower-energy X-rays with higher

resolution. SSC has two cameras - SSC-H and

SSC-Z, each has 16 CCD chips and is identical

to each other. It has a Field of view of

○

× 1.5

○

and an eﬀective area of 200 cm

MAXI is an all-sky survey experiment and has a larger

coverage of the sky. It has identiﬁed several X-ray

sources from the initial days of operations. It discovered

several new transient sources and made regular follow-

up observations of them. MAXI has decade-long light

curves of diﬀerent X-ray sources. MAXI contributed

signiﬁcantly to Tidal Disruption Event (TDE) studies,

which are cataclysms where stars are torn apart by

supermassive black holes (SMBHs).

3.5 Reference

About X-ray Astronomy Satellite ”Suzaku”

(ASTRO-EII)

Suzaku Mission Overview

X-Ray Telescopes (XRT)

The Suzaku Technical Description

The X-Ray Observatory Suzaku

X-Ray Spectrometer (XRS)

Hard X-ray Detector (HXD)

The Hard X-ray Detector

Tadayuki Takahashi, Keiichi Abe, Manabu

Endo, Yasuhiko Endo, Yuuichiro Ezoe,

Yasushi Fukazawa, Masahito Hamaya, Shinya

Hirakuri, Soojing Hong, Michihiro Horii,

Hokuto Inoue, Naoki Isobe, Takeshi Itoh,

Naoko Iyomoto, Tuneyoshi Kamae, Daisuke

Kasama, Jun Kataoka, Hiroshi Kato, Madoka

Kawaharada, Naomi Kawano, Kengo Kawashima,

Satoshi Kawasoe, Tetsuichi Kishishita, Takao

Kitaguchi, Yoshihito Kobayashi, Motohide

Kokubun, Jun’ichi Kotoku, Manabu Kouda, Aya

Kubota, Yoshikatsu Kuroda, Greg Madejski,

Kazuo Makishima, Kazunori Masukawa, Yukari

Matsumoto, Takefumi Mitani, Ryohei Miyawaki,

Tsunefumi Mizuno, Kunishiro Mori, Masanori

Mori, Mio Murashima, Toshio Murakami,

Kazuhiro Nakazawa, Hisako Niko, Masaharu

Nomachi, Yuu Okada, Masanori Ohno, Kousuke

Oonuki, Naomi Ota, Hideki Ozawa, Goro Sato,

Shingo Shinoda, Masahiko Sugiho, Masaya

Suzuki, Koji Taguchi, Hiromitsu Takahashi,

Isao Takahashi, Shin’ichiro Takeda, Ken-ichi

Tamura, Takayuki Tamura, Takaaki Tanaka,

Chiharu Tanihata, Makoto Tashiro, Yukikatsu

Terada, Shin’ya Tominaga, Yasunobu Uchiyama,

Shin Watanabe, Kazutaka Yamaoka, Takayuki

Yanagida, Daisuke Yonetoku, Hard X-Ray

Detector (HXD) on Board Suzaku, Publications

of the Astronomical Society of Japan, Volume

59, Issue sp1, 30 January 2007, Pages S35–S51,

https://doi.org/10.1093/pasj/59.sp1.S35

Hirofumi Noda, Kazuo Makishima, Yuuichi

Uehara, Shin’ya Yamada, Kazuhiro Nakazawa

Suzaku Discovery of a Hard Component

Varying Independently of the Power-Law

Emission in MCG 6–30–15, Publications of

the Astronomical Society of Japan, Volume

63, Issue 2, 25 April 2011, Pages 449–458,

https://doi.org/10.1093/pasj/63.2.449

Suzaku

Cattaneo, P. W. and Rappoldi, A. and Argan, A.

and Barbiellini, G. and Boﬀelli, F. and Bulgarelli,

A. and Buonomo, B. and Cardillo, M. and Chen,

A. W. and Cocco, V. and Colafrancesco, S. and

D’Ammando, F. and Donnarumma, I. and Ferrari,

A. and Fioretti, V. and Foggetta, L. and Froysland,

T. and Fuschino, F. and Galli, M. and Gianotti,

F. and Giuliani, A. and Longo, F. and Lucarelli,

F. and Marisaldi, M. and Mazzitelli, G. and

Morselli, A. and Paoletti, F. and Parmigiani, N.

3.5 Reference

and Pellizzoni, A. and Piano, G. and Pilia, M.

and Pittori, C. and Prest, M. and Pucella, G. and

Quintieri, L. and Sabatini, S. and Tavani, M. and

Trifoglio, M. and Trois, A. and Valente, P. and

Vallazza, E. and Vercellone, S. and Verrecchia, F.

and Zambra, A Calibration of AGILE-GRID with

On-ground Data and Monte Carlo Simulations

The Astrophysical Journal

Feroci, M. and Costa, E. and Soﬃtta, P. and Del

Monte, E. and Di Persio, G. and Donnarumma, I.

and Evangelista, Y. and Frutti, M. and Lapshov,

I. and Lazzarotto, F. and Mastropietro, M. and

Morelli, E. and Pacciani, L. and Porrovecchio,

G. and Rapisarda, M. and Rubini, A. and

Tavani, M. and Argan, A. SuperAGILE: The

hard X-ray imager for the AGILE space mission

Nuclear Instruments and Methods in Physics

Research Section A: Accelerators, Spectrometers,

Detectors and Associated Equipment

MAXI

Monitor of All-sky X-ray Image (MAXI)

Tatehiro Mihara, Hiroshi Tsunemi, Hitoshi

Negoro MAXI : Monitor of All-sky X-ray Image

arxiv

Hiroshi Tomida, Hiroshi Tsunemi, Masashi

Kimura, Hiroki Kitayama, Masaru Matsuoka,

Shiro Ueno, Kazuyoshi Kawasaki, Haruyoshi

Katayama, Kazuhisa Miyaguchi, Kentaro Maeda,

Arata Daikyuji, Naoki Isobe Solid-State Slit

Camera (SSC) Aboard MAXI Publications of

the Astronomical Society of Japan, Volume

63, Issue 2, 25 April 2011, Pages 397–405,

https://doi.org/10.1093/pasj/63.2.397

Tatehiro Mihara, Motoki Nakajima, Mutsumi

Sugizaki, Motoko Serino, Masaru Matsuoka,

Mitsuhiro Kohama, Kazuyoshi Kawasaki,

Hiroshi Tomida, Shiro Ueno, Nobuyuki Kawai,

Jun Kataoka, Mikio Morii, Atsumasa Yoshida,

Kazutaka Yamaoka, Satoshi Nakahira, Hitoshi

Negoro, Naoki Isobe, Makoto Yamauchi,

Ikuya Sakurai Gas Slit Camera (GSC)

onboard MAXI on ISS Publications of the

Astronomical Society of Japan, Volume 63, Issue

sp3, 25 November 2011, Pages S623–S634,

https://doi.org/10.1093/pasj/63.sp3.S623

About the Author

Aromal P is a research scholar in

Department of Astronomy, Astrophysics and Space

Engineering (DAASE) in Indian Institute of

Technology Indore. His research mainly focuses on

studies of Thermonuclear X-ray Bursts on Neutron star

surface and its interaction with the Accretion disk and

Corona.

The Hunt for the Cosmic Radio Lines of

Neutral Hydrogen

by Linn Abraham

airis4D, Vol.3, No.5, 2025

www.airis4d.com

The universe communicates with us not just

through the visible light our eyes can see, but across the

entire electromagnetic spectrum. The dawn of radio

astronomy opened an entirely new window onto the

cosmos, beginning with pioneers like Karl Jansky,

who accidentally discovered a “steady hiss type static

of unknown origin” in 1932 while studying interference

on transatlantic radio telephone service. Jansky’s work

revealed radio waves apparently coming from space,

particularly from the plane of the Milky Way. Despite

his recognition of the importance of this discovery,

his work was not immediately appreciated by radio

engineers, astronomers, or physicists.

Following Jansky, individuals like Grote Reber

took up the challenge, building dedicated radio

telescopes in his backyard. Reber produced the ﬁrst

radio contour maps of the sky, beautifully outlining the

Milky Way and hints of discrete sources. His work

helped demonstrate the potential of studying the cosmos

at radio wavelengths. Early theoretical work sought

to explain the observed galactic background radiation,

considering mechanisms like thermal free-free emission

from interstellar gas. However, calculations showed that

Jansky’s observed brightness temperatures of around

100,000 K at low frequencies could not be explained

by thermal emission from gas at typical interstellar

temperatures of

∼

10,000 K. This discrepancy pointed

towards non-thermal processes, leading later to the

suggestion of the synchrotron mechanism, involving

cosmic rays in galactic magnetic ﬁelds.

Building on these foundational observations

and techniques, radio astronomers sought to extend

spectroscopic analysis – the study of speciﬁc

wavelengths or frequencies – into the radio domain,

much like optical astronomers used it to determine

stellar properties. A crucial goal in this quest was

the search for a single, profoundly important cosmic

radio signal: the 21 cm line of atomic hydrogen.

4.1 The Bold Prediction (Amidst

Darkness)

The intellectual journey toward discovering this

speciﬁc radio line began in a surprisingly challenging

environment: Nazi-occupied Holland during World War

II. Amidst these diﬃcult circumstances, a student named

Hendrik van de Hulst at Leiden chose to continue

his studies after his professor was detained. Working

with J.H. Oort, who was impressed by the potential of

radio waves for studying the galaxy’s structure (having

learned about Reber’s reports from a smuggled journal),

Van de Hulst tackled the theoretical problem of what

speciﬁc radio signals interstellar hydrogen might emit.

Van de Hulst’s theoretical work is described as

“remarkable both for its scientiﬁc prescience and for

the conditions under which it was produced”. While

he considered other possibilities, his most signiﬁcant

contribution was the ﬁrst discussion of the implications

of the 21 cm hyperﬁne line of atomic hydrogen. This

line arises from a speciﬁc, low-energy transition within

the neutral hydrogen atom. Van de Hulst calculated

4.2 Independent Conﬁrmation and Other Ideas

the wavelength to be “21.1 cm, corresponding to a

frequency of 1420.4 MHz”. He noted that receiver

sensitivity would need to improve signiﬁcantly for

detection, acknowledging the speculative nature of

this transition but recognizing its immense potential

given hydrogen’s abundance and the ideal wavelength

for interstellar penetration.

4.2 Independent Conﬁrmation and

Other Ideas

Working independently in the Soviet Union, Iosif

Shklovsky was also motivated to predict cosmic radio

lines after seeing a brief mention of Van de Hulst’s ideas.

Even without access to the original article, Shklovsky

performed his own calculations concerning the 21 cm

line in a “largely independent manner”.

Shklovsky’s paper was the ﬁrst to calculate the

probability for the hyperﬁne transition, achieving a

result “oﬀ by only a factor 4” from the correct value.

He argued for collisional excitation of the line and

demonstrated the “feasibility of detection of the line

with available equipment”.

Remarkably, Shklovsky’s work also included an

“entirely original second portion” concerning potential

radio line radiation from deuterium and, signiﬁcantly,

interstellar molecules like OH and CH. He was

“enthusiastic about the odds for detection” of these

molecular transitions. This part of his work, anticipating

the “rich ﬁeld of galactic microwave spectroscopy” by

two decades, wasn’t widely followed up for several

years.

4.3 The Breakthrough Discovery

Despite these theoretical predictions and

encouraging calculations, the 21 cm line remained

undetected for several years due to the “diﬃculties

of receiver technology”. When the discovery ﬁnally

happened in 1951, it occurred “as so often happens

in modern science,” with detection and conﬁrmation

achieved by three independent groups scattered

around the globe within a very short time.

In the United States, H. I. Ewen and E. M. Purcell

were conducting thesis research at Harvard. They used a

large horn antenna “stuck out a window” and their initial

observations showed neutral hydrogen concentrated

towards the galactic plane. However, their equipment’s

limitations in resolution and frequency coverage meant

they detected only the “tip of the iceberg” of the signal,

missing its full structure and galactic rotation shifts.

In Holland, C.A. Muller and J.H. Oort were

driven to detect the line to study the structure of our

galaxy. They utilized a 7.5 m Wurzburg paraboloid

antenna abandoned by the German army. Their receiver

had similar sensitivity to Ewen’s, but their frequency-

switching interval was also not fully adequate for

capturing the full line proﬁles. Nevertheless, they

successfully measured frequency shifts of the peak

intensity at diﬀerent galactic longitudes.

The third group in Australia, spurred by immediate

notiﬁcation from Ewen and Purcell, quickly assembled

equipment and detected the line within months. In

a spirit of scientiﬁc cooperation, Ewen and Purcell

insisted that the initial reports from all three groups

“simultaneously appear”, which they did in the 1

September 1951 issue of Nature.

4.4 The Power of the 21 cm Line

The detection of the 21 cm hydrogen line was a

transformative event for astronomy. Neutral hydrogen

is the most abundant element in the universe, and this

line provided a unique tool to study its vast clouds

between the stars.

Crucially, unlike visible light, radio waves at 21

cm wavelength can penetrate the interstellar dust that

obscures much of the Milky Way’s structure from optical

view. This capability allowed astronomers to map the

structure of our own galaxy in unprecedented detail.

By measuring the Doppler shifts of the 21 cm line,

astronomers could determine the velocities of hydrogen

clouds, revealing the Milky Way’s rotation and spiral

structure. Oort himself had pioneered principles of

galactic structure and dynamics that could now be

applied using this new tool. Subsequent large-scale

surveys provided the ﬁrst comprehensive look at this

4.5 Conclusion

spiral structure.

This period also saw the discovery and initial

study of discrete radio sources, often initially called

“radio stars”. Examples include Cassiopeia A (Cas

A), Cygnus A (Cyg A), Taurus A (Tau A), and Virgo

A (Vir A). Pioneers like Hey, Parsons, and Phillips

discovered intensity variations in Cyg A, opening

up a new line of investigation. Bolton and Stanley

determined that the Cyg A source had a small size. Later,

through painstaking work involving precise position

measurements, these sources were optically identiﬁed,

such as Tau A with the Crab Nebula supernova remnant,

Vir A with a galaxy, and most notably, Cyg A with a

distant, peculiar galaxy, and Cas A with a new type of

galactic emission nebulosity. The discovery of Cyg A

as an extragalactic source had signiﬁcant implications

for cosmology.

Early investigations also included attempts

to detect the Sun at radio wavelengths, initially

unsuccessfully. Success came during WWII through

the accidental detection by James Hey using radar

equipment and independently by Grote Southworth.

These observations showed that the Sun emitted

surprisingly strong radio radiation, particularly

associated with sunspot activity. Techniques like

using interferometers, analogous to Michelson’s optical

interferometer, were developed to measure the sizes of

sources like the Sun and discrete sources, revealing, for

instance, that Cyg A had a complex, possibly double

structure. Other techniques like Dicke switching were

developed to improve receiver sensitivity.

The period from the late 19th century attempts

to detect solar radio waves through Jansky’s discovery

and Reber’s mapping, culminating in the prediction

and detection of the 21 cm hydrogen line, marked a

revolutionary era. It revealed a “quiescent and limited

Universe” in radio waves, enabling unprecedented

studies of our galaxy’s structure and paving the way for

the exploration of distant cosmic radio sources. This

journey, born from theoretical insight and enabled by

improving radio technology and innovative techniques,

demonstrates how pioneering work in radio astronomy

fundamentally changed our understanding of the

universe.

4.5 Conclusion

The journey from theoretical prediction by Van de

Hulst under wartime duress, to independent calculations

by Shklovsky, and ﬁnally, the near-simultaneous

detection by three groups across the globe, is a testament

to scientiﬁc ingenuity and perseverance. The discovery

of the 21 cm hydrogen line, was a watershed moment.

It provided astronomers with an indispensable tool for

studying the most abundant element in the universe and,

critically, for mapping the structure of our own galaxy, a

task impossible with optical astronomy alone due to dust

obscuration. This breakthrough, born from theoretical

insight and enabled by improving radio technology,

perfectly embodies the theme of how pioneering work in

radio techniques and the interpretation of cosmic signals

revolutionized our understanding of the universe. The

21 cm line stands as a prime example of the incredible

secrets the radio sky held, waiting to be unlocked.

References

[Sullivan(1982)]

Woodruﬀ Turner Sullivan. Classics

in Radio Astronomy. Springer Netherlands,

Dordrecht, 1982. ISBN 978-94-009-7754-9 978-

94-009-7752-5. doi: 10.1007/978-94-009-7752-5.

[Pritchard and Loeb(2012)]

Jonathan R Pritchard and

Abraham Loeb. 21 cm cosmology in the 21st

century. Reports on Progress in Physics, 75(8):

086901, August 2012. ISSN 0034-4885, 1361-

6633. doi: 10.1088/0034-4885/75/8/086901.

[Peebles(2020)]

P. J. E. Peebles. Quantum Mechanics.

Princeton University Press, Princeton, New Jersey,

ﬁrst paperback printing edition, 2020. ISBN 978-

0-691-20982-1 978-0-691-20673-8.

[Kraus(1966)]

John D. Kraus. Radio Astronomy.

January 1966.

[Condon and Ransom(2016)]

J. J. Condon and

Scott M. Ransom. Essential Radio Astronomy.

Princeton Series in Modern Observational

Astronomy. Princeton University Press, Princeton,

2016. ISBN 978-0-691-13779-7.

REFERENCES

About the Author

Linn Abraham is a researcher in Physics,

specializing in A.I. applications to astronomy. He is

currently involved in the development of CNN based

Computer Vision tools for prediction of solar ﬂares

from images of the Sun, morphological classiﬁcations

of galaxies from optical images surveys and radio

galaxy source extraction from radio observations.

Type I Supernovae: Stellar Explosions

Without Hydrogen

by Sindhu G

airis4D, Vol.3, No.5, 2025

www.airis4d.com

5.1 Introduction

Supernovae are among the most powerful and

dramatic phenomena in the universe. They are stellar

explosions that can brieﬂy outshine an entire galaxy,

releasing an immense amount of energy and dispersing

elements into the interstellar medium. Supernovae are

generally classiﬁed into two main types based on their

spectral features: Type I and Type II. The distinguishing

feature of Type I supernovae is the absence of hydrogen

lines in their spectra. These events play a critical role

in astrophysics, from the enrichment of the interstellar

medium to their use as standard candles for measuring

cosmological distances.

Type I supernovae are further subdivided into three

categories—Type Ia, Ib, and Ic—based on the presence

or absence of other elements in their spectra, such as

silicon and helium. Among them, Type Ia supernovae

are especially signiﬁcant because of their consistent

peak luminosity, which makes them valuable tools in

cosmology.

5.2 Classiﬁcation and Spectral

Characteristics

5.2.1 Absence of Hydrogen

The classiﬁcation into Type I is based on the lack

of hydrogen Balmer lines in the optical spectrum near

the peak of the light curve. This contrasts with Type II

supernovae, which show prominent hydrogen lines and

Figure 1: G299 Type Ia supernova remnant. (Image

Credit: NASA/CXC/U.Texas. )

Figure 2: The Type Ib supernova SN 2008D in galaxy

NGC 2770, shown in X-ray (left) and visible light

(right). (Image Credit:NASA / Swift Science Team /

Stefan Immler - NASA. )

5.3 Progenitors and Explosion Mechanisms

originate from massive stars that retain their hydrogen

envelopes.

5.2.2 Subtypes

Type Ia Supernovae

These supernovae are characterized by a strong

silicon absorption line at 6150

A. Type Ia events result

from the thermonuclear explosion of a white dwarf

in a binary system, typically a carbon-oxygen white

dwarf that accretes matter from a companion star until

it approaches the Chandrasekhar limit (

∼

1.4 solar

masses).

Type Ib and Ic Supernovae

These are core-collapse supernovae of massive

stars that have lost their outer envelopes. Type Ib shows

strong helium lines, while Type Ic lacks both hydrogen

and helium. The progenitors are often Wolf-Rayet stars

that have shed their outer layers through stellar winds

or interactions with a binary companion.

5.3 Progenitors and Explosion

Mechanisms

5.3.1 Type Ia Progenitors

There are two main scenarios proposed for Type

Ia progenitors:

Single-Degenerate Model: A white dwarf

accretes matter from a non-degenerate companion

(main-sequence or red giant star). When it

approaches the Chandrasekhar limit, it undergoes

a thermonuclear runaway, leading to a supernova

explosion.

Double-Degenerate Model: Two white dwarfs

in a binary system merge due to gravitational

wave emission. If the resulting mass exceeds

the Chandrasekhar limit, it can lead to a similar

thermonuclear explosion.

Recent observations and simulations suggest that

both channels may contribute to the observed population

of Type Ia supernovae, but the relative frequency

remains an area of active research.

5.3.2 Type Ib/Ic Progenitors

Type Ib and Ic supernovae originate from massive

stars (initial masses

8 solar masses) that have

undergone signiﬁcant mass loss. In these cases, the

core of the star collapses once nuclear fuel is exhausted,

leading to the formation of a neutron star or black hole.

The outer layers are ejected in the supernova explosion.

5.4 Light Curves and Observational

Features

5.4.1 Type Ia Light Curves

Type Ia supernovae exhibit a well-deﬁned light

curve characterized by a rapid rise to peak brightness

followed by a slower decline. The peak luminosity

is powered by the radioactive decay of

Ni to

and eventually to

Fe. The uniformity of Type Ia

light curves, after applying corrections for light curve

shape and color, enables their use as standard candles

in cosmology.

5.4.2 Type Ib/Ic Light Curves

The light curves of Type Ib and Ic supernovae are

more diverse and typically less luminous than those of

Type Ia. They also show faster decline rates. The energy

source is similar—radioactive decay of nickel—but the

diﬀerences arise due to the progenitor structure and

explosion mechanism.

5.5 Cosmological Signiﬁcance

Type Ia supernovae are essential tools for

measuring cosmic distances. Their consistent peak

brightness allows astronomers to determine distances

with relatively low uncertainty. Observations of distant

Type Ia supernovae in the late 1990s led to the

groundbreaking discovery that the universe’s expansion

is accelerating, a ﬁnding that earned the 2011 Nobel

Prize in Physics. This acceleration is attributed to a

mysterious component of the universe known as dark

energy.

5.6 Current Research and Open Questions

The use of Type Ia supernovae as standard candles

involves several corrections, including:

Stretch correction (light curve width–luminosity

relation).

Color correction (dust extinction and intrinsic

color variations).

Host galaxy correction (metallicity and star

formation eﬀects).

5.6 Current Research and Open

Questions

Despite their importance, several questions remain

about Type I supernovae:

What is the dominant progenitor system for Type

Ia supernovae?

How do metallicity and environment aﬀect

supernova properties?

Can we accurately model the explosion

mechanisms in 3D simulations?

How do Type Ib and Ic progenitors evolve, and

what is the role of binary interactions?

Ongoing surveys such as the Zwicky Transient

Facility (ZTF), Pan-STARRS, and the upcoming Vera

C. Rubin Observatory are providing massive datasets

that help answer these questions. Spectroscopic

follow-up, polarimetric observations, and gravitational

wave astronomy are also contributing to a deeper

understanding.

5.7 Conclusion

Type I supernovae are not only spectacular

astrophysical events but also critical tools for

understanding the cosmos. From the thermonuclear

explosions of white dwarfs to the core-collapse of

massive stars, they provide insight into stellar evolution,

nucleosynthesis, and the large-scale structure of the

universe. With new observational capabilities and

improved theoretical models, our understanding of

these phenomena continues to grow, promising exciting

discoveries in the years ahead.

References:

Observational Signatures of Type Ia Supernovae

Type Ia supernova

Type Ib and Ic supernovae

The double-degenerate model for the progenitors

of Type Ia supernovae

Single Degenerate Models for Type Ia

Supernovae

The prolonged death of light from type Ia

supernovae

Modelling Type Ia Supernova Light Curves

Towards a better understanding of the evolution

of Wolf–Rayet stars and Type Ib/Ic supernova

progenitors

ZTF counts more than 10,000 supernovae

Type Ia Supernovae: How DES Used Exploding

Stars to Measure Dark Energy

Type Ia supernovae as stellar endpoints and

cosmological tools

The diﬀerent types of supernovae explained

Supernovae Ib and Ic from the explosion of

helium stars

Evolutionary Models for Type Ib/c Supernova

Progenitors

Type Ib and Ic Supernovae: Models and Spectra

Near-infrared Spectral Properties of Type Ib/Ic

Supernova Progenitors and Implications for

JWST and NGRST Observations

About the Author

Sindhu G is a research scholar in Physics

doing research in Astronomy & Astrophysics. Her

research mainly focuses on classiﬁcation of variable

stars using diﬀerent machine learning algorithms. She

is also doing the period prediction of diﬀerent types

of variable stars, especially eclipsing binaries and on

the study of optical counterparts of X-ray binaries.

Part II

Biosciences

Beyond Morphology: How Molecular

Taxonomy is Reshaping Species Identiﬁcation

by Geetha Paul

airis4D, Vol.3, No.5, 2025

www.airis4d.com

1.1 Introduction

For centuries, the science of taxonomy - the

classiﬁcation of living organisms - relied almost

exclusively on observable morphological characteristics.

Biologists painstakingly documented and compared

physical traits such as shape, size, colour, anatomical

structures, and developmental patterns to group

organisms and infer evolutionary relationships. This

morphological approach, pioneered by Carl Linnaeus

in the 18th century, formed the foundation of biological

classiﬁcation and served science well for generations.

However, as our understanding of biological

diversity deepened, the limitations of morphology-

based taxonomy became increasingly apparent. Many

species exhibit remarkable phenotypic plasticity,

where genetically identical organisms can display

vastly diﬀerent physical characteristics depending on

environmental conditions. Conversely, convergent

evolution often produces similar morphological features

in unrelated species facing similar ecological pressures.

Perhaps most challenging are cryptic species complexes

- groups of organisms that appear identical to human

observers but are genetically distinct species.

These challenges came to a head in the latter

half of the 20th century as new technologies revealed

contradictions between morphological classiﬁcations

and molecular evidence. The development of protein

electrophoresis in the 1960s and DNA sequencing in

the 1970s provided the ﬁrst glimpses of a hidden world

of genetic variation that didn’t always correspond to

visible diﬀerences. This technological revolution set

the stage for the emergence of molecular taxonomy as a

distinct discipline.

Molecular taxonomy represents a paradigm shift

in how we deﬁne and identify species. By comparing

DNA, RNA, and protein sequences, researchers can

peer directly into an organism’s genetic blueprint,

uncovering evolutionary relationships that may be

obscured at the morphological level. This approach has

resolved numerous taxonomic controversies that had

persisted for decades. For instance, what were once

considered single, widespread species have frequently

been revealed to be complexes of multiple genetically

distinct species. Conversely, organisms classiﬁed as

separate species based on morphology have sometimes

been shown to represent mere variants within a single

genetically cohesive population.

The impact of molecular taxonomy extends far

beyond academic debates. In conservation biology,

it helps identify evolutionarily signiﬁcant units for

protection. In medicine, it enables more accurate

identiﬁcation of pathogen strains. In agriculture, it

improves our understanding of crop wild relatives

and pests. Perhaps most fundamentally, molecular

taxonomy has transformed our understanding of

biodiversity, revealing that our planet hosts far more

species, particularly microbial ones, than we ever

imagined based on morphological studies alone.

As we stand today, molecular taxonomy

has become an indispensable tool in modern

biology, complementing and superseding traditional

1.2 Key Applications of Molecular Taxonomy

Figure 1: DNA barcoding Procedure

Image courtesy https://www.researchgate.net/publication/382871147 DNA Barcoding and Its App

lications

morphological approaches in many cases. The

following sections explore how this revolution came

about, its major applications, and the exciting

possibilities it holds for the future of species

identiﬁcation and classiﬁcation. From DNA barcoding

to phylogenomics, we will examine how molecular data

reshapes our understanding of life’s diversity at its most

fundamental level.

1.1.1 The Shift from Morphology to

Molecules

Traditional taxonomy relies on anatomical and

morphological comparisons, which can be misleading

due to: Convergent evolution (unrelated species

developing similar traits), High phenotypic plasticity

(single species exhibiting varied forms), Cryptic species

(genetically distinct organisms that appear identical).

1.1.2 The Rise of Molecular Techniques

Molecular taxonomy overcomes these challenges

by analysing genetic diﬀerences. Key advances include:

DNA barcoding (e.g., CO1 for animals, ITS for

fungi, rbcl for plants), High-throughput sequencing

(NGS) enabling large-scale genomic comparisons,

Phylogenomics, using hundreds of genes to reconstruct

evolutionary trees.

1.2 Key Applications of Molecular

Taxonomy

Discovering Hidden Biodiversity: Molecular Tools

Revealing Nature’s Secrets

1.2.1 Cryptic Species Unmasked

Molecular taxonomy has revolutionized

our understanding of species boundaries by

exposing widespread cryptic diversity - cases

where morphologically identical organisms are actually

genetically distinct species. A classic example comes

from Eleutherodactylus frogs in the Caribbean, where

what appeared to be a single widespread species was

revealed through mitochondrial DNA analysis to

comprise at least 12 distinct evolutionary lineages,

each warranting species status (Heinicke et al., 2007).

Similar patterns have been found across taxa, Insects:

16% of European butterﬂies have cryptic sister species

(Vila et al., 2011) Marine life: 33% of surveyed ﬁsh

species hide cryptic diversity (Bickford et al., 2007)

Plants: 23% of tropical trees show cryptic speciation

(Dick & Webb, 2012).

These discoveries fundamentally alter biodiversity

estimates and conservation priorities, as what was

thought to be one widespread, secure species may

actually be multiple range-restricted threatened species.

1.2.2 The Microbial Dark Matter Revolution

Before 16S rRNA sequencing, microbiologists

could culture and study less than 1% of environmental

microbes. Molecular approaches have increased known

bacterial phyla from 12 to over 100 (Hugenholtz et

al., 2016), revealed the Candidate Phyla Radiation,

comprising 15-30% of bacterial diversity (Brown et

al., 2015). As early as 2007, Fierer et al. noted

that a single gram of soil can contain

10,000

microbial species (Fierer et al., 2007),The Earth

Microbiome Project has now cataloged over 300,000

microbial OTUs (operational taxonomic units), with

most representing uncultured lineages (Thompson

et al., 2017). This hidden diversity has profound

1.3 Challenges and Future Directions

implications for ecosystem functioning, biotechnology,

and understanding the origins of life.

1.2.3 Resolving Taxonomic Conﬂicts:

Molecular Data as the Ultimate Arbiter

Reclassifying Iconic Species

African elephants: Mitochondrial and nuclear

DNA proved Loxodonta africana (savanna) and L.

cyclotis (forest) diverged 2-7 million years ago,

warranting separate species status (Roca et al., 2015),

Giraﬀes: Genomic data revealed four distinct species

rather than one (Fennessy et al., 2016), Orcas:

eDNA studies suggest at least three separate species

exist (Morin et al., 2010). These reclassiﬁcations

dramatically aﬀect conservation status assessments and

management strategies.

1.2.4 Hybridisation Detection and Its

Consequences

Molecular markers excel at identifying hybrids

where morphology fails. Canid hybrids: SNPs

distinguish gray wolf (Canis lupus) × coyote (C. latrans)

hybrids, crucial for endangered wolf conservation

(vonHoldt et al., 2016), Coral reefs: RADseq revealed

widespread hybridization among Acropora species, with

implications for reef resilience (Richards et al., 2018),

Plants: Chloroplast DNA tracks historical hybridization

in oaks, explaining their rapid adaptation (Hipp et al.,

2020). Hybrid zones serve as natural laboratories for

studying speciation, and molecular tools are essential

for mapping these dynamic boundaries.

1.2.5 Conservation and Forensics: Molecular

Taxonomy in Action

Combating Wildlife Traﬃcking

DNA barcoding has become a frontline tool against

illegal wildlife trade. Shark ﬁns: CO1 barcoding

identiﬁed 71 species in Hong Kong markets, including

endangered scalloped hammerheads (Carde

nosa et al.,

2018). Timber: matK and rbcL barcodes expose illegal

logging of protected Dalbergia and Pterocarpus species

(Dormontt et al., 2015). Caviar: Microsatellites verify

Figure 2: Application of Chloroplast DNA Barcodes

In Various Fields

species origin in 30% of commercial products (Birstein

et al., 2005).

Interpol’s Wildlife Crime Working Group now

routinely employs genetic forensics, with conviction

rates increasing 300% since 2015 (INTERPOL, 2021).

1.2.6 Genetic Rescue of Endangered Species

Population genomics guides critical conservation

decisions: Florida panther (Puma concolor coryi):

Introduction of Texas cougars based on genetic

data increased heterozygosity by 90% and reduced

abnormalities (Johnson et al., 2010).Kakapo parrots:

Genome sequencing informs breeding pairs to maximize

genetic diversity (Dussex et al., 2021). Coral reefs: SNP

arrays identify heat-resistant Acropora genotypes for

reef restoration (Matz et al., 2018)

The IUCN now recommends genomic assessments

for all threatened species, recognising that genetic

diversity predicts long-term viability (Hoban et al.,

2020). Molecular taxonomy thus bridges the gap

between species discovery and species survival.

1.3 Challenges and Future Directions

Cost and accessibility: Advanced sequencing

remains expensive in developing regions. Data

interpretation: Phylogenetic conﬂicts arise from

horizontal gene transfer (HGT) or incomplete lineage

sorting. Ethical considerations: Should genetic

divergence alone deﬁne species, or should ecology

and morphology still play a role. Future innovations,

like portable sequencers (e.g., Oxford Nanopore) and

1.4 Conclusion

AI-driven phylogenetics, promise to democratise and

reﬁne the ﬁeld.

1.4 Conclusion

Molecular taxonomy has revolutionised our

understanding of biodiversity by transcending

the limitations of traditional morphology-

based classiﬁcation. Through DNA barcoding,

phylogenomics, and high-throughput sequencing, it

has uncovered cryptic species, resolved long-standing

taxonomic conﬂicts, and revealed the astonishing

diversity of microbial life. Beyond academic

signiﬁcance, these tools have become indispensable

for conservation—combating wildlife traﬃcking,

guiding genetic rescue eﬀorts, and informing species

management policies. As portable sequencing and

AI-driven analysis democratize access to genetic data,

molecular taxonomy is poised to address emerging

challenges, from delineating species in microbes

to reconciling genomic and ecological data. This

paradigm shift has not only reﬁned our classiﬁcation

systems but fundamentally transformed how we

perceive, study, and protect life on Earth, proving that

the true boundaries of biodiversity often lie hidden in

the genome. Moving forward, molecular approaches

will remain central to both understanding evolution

and mitigating biodiversity loss in an era of rapid

environmental change.

References

https://doi.org/10.1038/nature14486

https://doi.org/10.1016/j.tree.2006.11.004

https://doi.org/10.1007/978-1-61779-591-6 18

https://doi.org/10.1128/AEM.00358-07

https://doi.org/10.1073/pnas.0611051104

https://doi.org/10.1101/cshperspect.a018085

https://doi.org/10.1111/j.1439-

0426.2005.00664.x

https://doi.org/10.1038/nature24621

https://doi.org/10.1016/j.biocon.2020.108654

https://www.interpol.int/en/Crimes/Environmental-

crime/Wildlife-crime

https://doi.org/10.1126/science.1192891

Hebert, P. D., Cywinska, A., Ball, S. L., &

deWaard, J. R. (2003). Biological identiﬁcations

through DNA barcodes. Proceedings of the Royal

Society B: Biological Sciences, 270(1512), 313-321.

Woese, C. R., Kandler, O., & Wheelis, M. L.

(1990).Towards a natural system of organisms: Proposal

for the domains Archaea, Bacteria, and Eucarya.

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87(12), 4576-4579.

Hillis, D. M., Moritz, C., & Mable, B. K. (1996).

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The Barcode of Life Data System. Molecular Ecology

Notes, 7(3), 355-364.

About the Author

Geetha Paul is one of the directors of

airis4D. She leads the Biosciences Division. Her

research interests extends from Cell & Molecular

Biology to Environmental Sciences, Odonatology, and

Aquatic Biology.

Part III

Computer Programming

Classifying Parallelism: Part-2

by Ajay Vibhute

airis4D, Vol.3, No.5, 2025

www.airis4d.com

1.1 Introduction

As discussed in earlier sections, parallelism can

be implemented through various models that distribute

computation across multiple processors or tasks, such

as data and task parallelism. However, there are also

more detailed forms of parallelism that take advantage

of the speciﬁc capabilities of individual processor

cores, oﬀering further performance improvements. By

exploring these lower-level parallelism techniques, we

can achieve additional optimization within each core,

resulting in a signiﬁcant boost in overall throughput and

a reduction in the time required to perform complex

operations.

These ﬁner levels of parallelism include bit-

level, instruction-level, and thread-level parallelism.

Each of these focuses on diﬀerent aspects of how

instructions are handled within the processor, providing

distinct opportunities for optimization at various stages

of the computational process. In the following

subsections, we will explore these foundational levels of

parallelism, emphasizing their strong connection with

the processor’s internal architecture and their critical

role in achieving high-performance computing.

1.2 Bit-Level Parallelism

Bit-level parallelism is a form of parallelism that

focuses on the simultaneous processing of individual

bits within larger data units. This capability is

primarily driven by the processor’s register width, which

determines the number of bits the processor can operate

on concurrently in a single operation. In traditional 8-bit

or 16-bit processors, operations could only be performed

on data in chunks of 8 or 16 bits. The advancement

from 8-bit and 16-bit processors to today’s prevalent

32-bit and 64-bit designs has signiﬁcantly enhanced the

capacity for parallel bit manipulation, directly resulting

in improved performance.

Bit-level parallelism proves particularly

advantageous in tasks that heavily utilize bitwise

operations, such as the complex calculations in

cryptography (exempliﬁed by AES), algorithms used

for data compression, and certain techniques in signal

processing. For example, by increasing the processor’s

data-handling capacity from 32 to 64 bits, the number

of bits processed in parallel for these operations

doubles, leading to substantial speedups.

Furthermore, the eﬃciency of bit-level parallelism

can be increased through the integration of SIMD

(Single Instruction, Multiple Data) units, which enable

the parallel execution of the same bitwise instruction

across multiple data elements. While bit-level

parallelism by itself may not provide as signiﬁcant

a speedup as higher levels of parallelism, it plays a vital

role in optimizing performance, especially in tasks that

require extensive low-level data manipulation.

1.3 Instruction-Level Parallelism

Instruction-Level Parallelism (ILP), ﬁgure 1,

allows a processor to execute multiple instructions

simultaneously within a single cycle. Unlike higher-

level parallelism models, which focus on distributing

entire tasks or datasets across multiple processors,

ILP optimizes the performance of a single processor

1.4 Thread-Level Parallelism

by increasing the number of instructions that can

be executed in parallel. Modern processors use

Figure 1: Instruction Level parallelism

various techniques, such as pipelining and out-of-

order execution, to achieve ILP. In pipelining, the

execution of instructions is divided into stages (e.g.,

fetching, decoding, executing, and writing back results),

with each stage processing a diﬀerent instruction.

By overlapping the stages of multiple instructions,

pipelining enables the concurrent execution of several

instructions within the same clock cycle, signiﬁcantly

increasing throughput.

Out-of-order execution further enhances ILP by

allowing the processor to execute instructions that are

not dependent on each other, even if they appear later

in the instruction stream. This feature is especially

useful in avoiding pipeline stalls caused by data hazards,

where instructions depend on the results of previous

instructions.

Despite its potential, the eﬀectiveness of ILP

is restricted by several factors, including instruction

dependencies, the availability of execution units, and

hardware constraints. For example, data hazards (where

one instruction depends on the output of another) can

limit the degree of parallelism achievable through ILP.

Moreover, control hazards, which occur when branching

instructions alter the ﬂow of execution, can also lead to

pipeline stalls and reduce eﬃciency. Modern processors

use techniques such as branch prediction and speculative

execution to address these issues, but the degree of ILP

remains constrained by the inherent characteristics of

the instruction stream.

1.4 Thread-Level Parallelism

Thread-level parallelism (TLP), ﬁgure 2, leverages

the multi-core design of contemporary processors

by enabling the simultaneous execution of multiple

threads. A thread represents an independent sequence

of instructions that can be executed in parallel with

others. By running multiple threads concurrently

on diﬀerent processor cores, TLP can signiﬁcantly

increase computational throughput, particularly in multi-

threaded applications that are well-suited to this model

of parallelism. TLP can be implemented using various

Figure 2: Thread Level parallelism

architectural approaches, including shared-memory

architectures—where multiple threads access a common

memory space—and distributed-memory systems, in

which each processor or core operates independently

with its own local memory. The advent of multi-core

processors has made TLP one of the most eﬀective

forms of parallelism in modern computing, as it allows

software to exploit concurrency inherent in parallel

workloads.

Maximizing the eﬃciency of TLP requires careful

management of synchronization and shared data

access. Without robust synchronization mechanisms,

concurrent threads may access shared resources

unsafely, resulting in race conditions and potentially

leading to unpredictable behavior or system errors.

To mitigate such issues, synchronization primitives

such as locks, semaphores, and atomic operations

are commonly employed. Additionally, maintaining

balanced workloads across threads is essential; uneven

1.5 Summary

task distribution can lead to idle cores and reduced

overall eﬃciency.

Although TLP oﬀers substantial performance

beneﬁts for applications with high degrees of intrinsic

parallelism, it is not universally applicable. It is

generally less eﬀective for problems characterized by

sequential logic or strong interdependencies between

operations. In such cases, the overhead associated with

managing threads—such as spawning, synchronization,

and coordination—can introduce delays that diminish

or negate potential performance gains.

1.5 Summary

In summary, bit-level, instruction-level, and thread-

level parallelism represent fundamental approaches

for optimizing the performance of modern processors.

By exploiting these diﬀerent forms of parallelism,

systems can achieve greater computational eﬃciency,

making them essential in areas ranging from high-

performance computing (HPC) to real-time processing

applications. While each level of parallelism oﬀers

distinct advantages, their combined use in multi-core,

superscalar processors allows for the eﬃcient handling

of diverse computational workloads. Understanding the

trade-oﬀs and limitations of each type of parallelism is

crucial for designing systems that eﬀectively harness

the power of modern hardware.

About the Author

Dr. Ajay Vibhute is currently working

at the National Radio Astronomy Observatory in

the USA. His research interests mainly involve

astronomical imaging techniques, transient detection,

machine learning, and computing using heterogeneous,

accelerated computer architectures.

About airis4D

Artiﬁcial Intelligence Research and Intelligent Systems (airis4D) is an AI and Bio-sciences Research Centre.

The Centre aims to create new knowledge in the ﬁeld of Space Science, Astronomy, Robotics, Agri Science,

Industry, and Biodiversity to bring Progress and Plenitude to the People and the Planet.

Vision

Humanity is in the 4th Industrial Revolution era, which operates on a cyber-physical production system. Cutting-

edge research and development in science and technology to create new knowledge and skills become the key to

the new world economy. Most of the resources for this goal can be harnessed by integrating biological systems

with intelligent computing systems oﬀered by AI. The future survival of humans, animals, and the ecosystem

depends on how eﬃciently the realities and resources are responsibly used for abundance and wellness. Artiﬁcial

intelligence Research and Intelligent Systems pursue this vision and look for the best actions that ensure an

abundant environment and ecosystem for the planet and the people.

Mission Statement

The 4D in airis4D represents the mission to Dream, Design, Develop, and Deploy Knowledge with the ﬁre of

commitment and dedication towards humanity and the ecosystem.

Dream

To promote the unlimited human potential to dream the impossible.

Design

To nurture the human capacity to articulate a dream and logically realise it.

Develop

To assist the talents to materialise a design into a product, a service, a knowledge that beneﬁts the community

and the planet.

Deploy

To realise and educate humanity that a knowledge that is not deployed makes no diﬀerence by its absence.

Campus

Situated in a lush green village campus in Thelliyoor, Kerala, India, airis4D was established under the auspicious

of SEED Foundation (Susthiratha, Environment, Education Development Foundation) a not-for-proﬁt company

for promoting Education, Research. Engineering, Biology, Development, etc.

The whole campus is powered by Solar power and has a rain harvesting facility to provide suﬃcient water supply

for up to three months of drought. The computing facility in the campus is accessible from anywhere through a

dedicated optical ﬁbre internet connectivity 24×7.

There is a freshwater stream that originates from the nearby hills and ﬂows through the middle of the campus.

The campus is a noted habitat for the biodiversity of tropical Fauna and Flora. airis4D carry out periodic and

systematic water quality and species diversity surveys in the region to ensure its richness. It is our pride that the

site has consistently been environment-friendly and rich in biodiversity. airis4D is also growing fruit plants that

can feed birds and provide water bodies to survive the drought.