INDIAN SPACE RESEARCH ORGANISATION :

The Indian Space Research Organisation (ISRO),is the primary body for space research under
the control of the Government of India, and one of the leading space research organizations in the
world. It was established in its modern form in 1969 as a result of coordinated efforts initiated earlier.
Taking into consideration its budget, it is among the most efficient space organizations on the
globe.Over the years, ISRO has conducted a variety of operations for both Indian and foreign clients.
ISRO's satellite launch capability is mostly provided by indigenous launch vehicles and launch sites. In
2008, ISRO successfully launched its first lunar probe, Chandrayaan-1, while future plans include
indigenous development of GSLV, manned space missions, further lunar exploration, and interplanetary
probes. ISRO has several field installations as assets, and cooperates with the international community
as a part of several bilateral and multilateral agreements.

STAR :

A star is a massive, luminous ball of plasma held together by gravity. At the end of its lifetime, a star
can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the
source of most of the energy on Earth. Other stars are visible from Earth during the night when they are
not outshone by the Sun or blocked by atmospheric phenomena. Historically, the most prominent stars
on the celestial sphere were grouped together into constellations and asterisms, and the brightest stars
gained proper names. Extensive catalogues of stars have been assembled by astronomers, which
provide standardized star designations.

For at least a portion of its life, a star shines due to thermonuclear fusion of hydrogen in its core
releasing energy that traverses the star's interior and then radiates into outer space. Almost all naturally
occurring elements heavier than helium were created by stars, either via stellar nucleosynthesis during
their lifetimes or by supernova nucleosynthesis when stars explode. Astronomers can determine the
mass, age, chemical composition and many other properties of a star by observing its spectrum,
luminosity and motion through space. The total mass of a star is the principal determinant in its
evolution and eventual fate. Other characteristics of a star are determined by its evolutionary history,
including diameter, rotation, movement and temperature. A plot of the temperature of many stars
against their luminosities, known as a Hertzsprung-Russell diagram (H–R diagram), allows the age and
evolutionary state of a star to be determined.

A star begins as a collapsing cloud of material composed primarily of hydrogen, along with helium and
trace amounts of heavier elements. Once the stellar core is sufficiently dense, some of the hydrogen is
steadily converted into helium through the process of nuclear fusion.[1] The remainder of the star's
interior carries energy away from the core through a combination of radiative and convective processes.
The star's internal pressure prevents it from collapsing further under its own gravity. Once the hydrogen
fuel at the core is exhausted, those stars having at least 0.4 times the mass of the Sun expand to become
a red giant, in some cases fusing heavier elements at the core or in shells around the core. The star then
evolves into a degenerate form, recycling a portion of the matter into the interstellar environment,
where it will form a new generation of stars with a higher proportion of heavy elements.

Formation :

Stars are formed within extended regions of higher density in the interstellar medium, although the
density is still lower than the inside of an earthly vacuum chamber. These regions are called molecular
clouds and consist mostly of hydrogen, with about 23–28% helium and a few percent heavier elements.
One example of such a star-forming region is the Orion Nebula.[54] As massive stars are formed from
molecular clouds, they powerfully illuminate those clouds. They also ionize the hydrogen, creating an
H II region.

Collapse :

An evolved, average-size star will now shed its outer layers as a planetary nebula. If what remains
after the outer atmosphere has been shed is less than 1.4 solar masses, it shrinks to a relatively tiny
object (about the size of Earth) that is not massive enough for further compression to take place, known
as a white dwarf.The electron-degenerate matter inside a white dwarf is no longer a plasma, even
though stars are generally referred to as being spheres of plasma. White dwarfs will eventually fade
into black dwarfs over a very long stretch of time.

Age :

Most stars are between 1 billion and 10 billion years old. Some stars may even be close to 13.7 billion
years old—the observed age of the universe. The oldest star yet discovered, HE 1523-0901, is an
estimated 13.2 billion years old.

The more massive the star, the shorter its lifespan, primarily because massive stars have greater
pressure on their cores, causing them to burn hydrogen more rapidly. The most massive stars last an
average of about one million years, while stars of minimum mass (red dwarfs) burn their fuel very
slowly and last tens to hundreds of billions of years.

Black Holes: What Are They?

Black holes are the evolutionary endpoints of stars at least 10 to 15 times as massive as the Sun. If
a star that massive or larger undergoes a supernova explosion, it may leave behind a fairly massive
burned out stellar remnant. With no outward forces to oppose gravitational forces, the remnant will
collapse in on itself. The star eventually collapses to the point of zero volume and infinite density,
creating what is known as a " singularity ". Around the singularity is a region where the force of gravity
is so strong that not even light can escape. Thus, no information can reach us from this region. It is
therefore called a black hole, and its surface is called the " event horizon ".
But contrary to popular myth, a black hole is not a cosmic vacuum cleaner. If our Sun was suddenly
replaced with a black hole of the same mass, the Earth's orbit around the Sun would be unchanged. (Of
course the Earth's temperature would change, and there would be no solar wind or solar magnetic
storms affecting us.) To be "sucked" into a black hole, one has to cross inside the Schwarzschild radius.
At this radius, the escape speed is equal to the speed of light, and once light passes through, even it
cannot escape.

Formation and evolution :

Considering the exotic nature of black holes, it may be natural to question if such bizarre objects
could exist in nature or to suggest that they are merely pathological solutions to Einstein's equations.
Einstein himself wrongly thought that black holes would not form, because he held that the angular
momentum of collapsing particles would stabilize their motion at some radius.This led the general
relativity community to dismiss all results to the contrary for many years. However, a minority of
relativists continued to contend that black holes were physical objects,and by the end of the 1960s, they
had persuaded the majority of researchers in the field that there is no obstacle to forming an event
horizon.

Once an event horizon forms, Roger Penrose proved that a singularity will form somewhere inside
it.Shortly afterwards, Stephen Hawking showed that many cosmological solutions describing the Big
Bang have singularities without scalar fields or other exotic matter (see Penrose-Hawking singularity
theorems). The Kerr solution, the no-hair theorem and the laws of black hole thermodynamics showed
that the physical properties of black holes were simple and comprehensible, making them respectable
subjects for research.[63] The primary formation process for black holes is expected to be the
gravitational collapse of heavy objects such as stars, but there are also more exotic processes that can
lead to the production of black holes.

Gravitational collapse :

Gravitational collapse occurs when an object's internal pressure is insufficient to resist the object's
own gravity. For stars this usually occurs either because a star has too little "fuel" left to maintain its
temperature through stellar nucleosynthesis, or because a star which would have been stable receives
extra matter in a way which does not raise its core temperature. In either case the star's temperature is
no longer high enough to prevent it from collapsing under its own weight (the ideal gas law explains
the connection between pressure, temperature, and volume).

The collapse may be stopped by the degeneracy pressure of the star's constituents, condensing the
matter in an exotic denser state. The result is one of the various types of compact star. Which type of
compact star is formed depends on the mass of the remnant — the matter left over after changes
triggered by the collapse (such as supernova or pulsations leading to a planetary nebula) have blown
away the outer layers. Note that this can be substantially less than the original star — remnants
exceeding 5 solar masses are produced by stars which were over 20 solar masses before the collapse.
If the mass of the remnant exceeds about 3–4 solar masses (the Tolman–Oppenheimer–Volkoff limit)—
either because the original star was very heavy or because the remnant collected additional mass
through accretion of matter—even the degeneracy pressure of neutrons is insufficient to stop the
collapse. After this, no known mechanism (except possibly quark degeneracy pressure, see quark star)
is powerful enough to stop the collapse and the object will inevitably collapse to a black hole.

This gravitational collapse of heavy stars is assumed to be responsible for the formation of stellar mass
black holes. Star formation in the young universe may have resulted in very heavy stars, which upon
their collapse would have produced black holes of up to 103 solar masses. These heavy black holes
could be the seeds of the supermassive black holes found in the centers of most galaxies.

While most of the energy released during gravitational collapse is emitted very quickly, an outside
observer does not actually see the end of this process. Even though the collapse takes a finite amount of
time from the reference frame of infalling matter, a distant observer sees the infalling material slow and
halt just above the event horizon, due to gravitational time dilation. Light from the collapsing material
takes longer and longer to reach the observer, with the light emitted just before the event horizon forms
delayed an infinite amount of time. Thus the external observer never sees the formation of the event
horizon; instead, the collapsing material seems to become dimmer and increasingly red-shifted,
eventually fading away.