Abstract they arise to observation of the most


interior of the sun and star using seismology, stars are playing the central
role in many areas of astronomy. Within the embrace of astronomy the coming
decade offers the opportunity to make significant progress in areas such as
multi-magnetic field. We will be able to test new models through qualitatively
new astero-seismology data. All these will enable us to solve open
questions.  Example: in nuclear
astrophysics in particular as they arise to observation of the most metal-poor
stars that are formed in early universe. We deliver comprehensive simulation
data sets, for example for applications in stellar population or galactic
chemical evolution. Taking advantage of new observatories, some in space, as
well as more powerful make significant new advances. In this paper the
evolution of stars, their properties and recent developments will be explained.

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word astronomy has a Greek origin, “Astro” means star and “nomy” from ‘nomous’
means laws. So literally astronomy means “The Laws of the Star”. Astrophysics
is a branch of astronomy that deals with the physical properties of heavily
bodies such as luminosity, size, mass, density, temperature and chemical
composition and their origin and evolution.

of Stars

is heavenly body having heat and light of its own (self-luminous). The sun is
the nearest star to us. Example: Alpha century, Sirius etc. Hertzsprung-Russell
Diagram gives us indication of the stellar evolutionary path from its birth to
its eventual death. The star is a delicate balance between the force of gravity
pulling in and pressure from the heat of fusion pushing out.

The stars are formed in the following way:

1.      Formation of  protostar

the beginning, the gases in the galaxies or inter stellar medium were mainly
hydrogen and helium. They are present at very low density and temperature about
100K. Since the gases were very cold, they formed very dense cloud in the
galaxies. The gas cloud was very cold, so the gravitational pull between the
various gas molecules was very large. Due to large gravitational force the gas
cloud started contracting as a whole. The gases were compressed so much that
they formed a highly condensed object called protostar. Thus protostar is a
highly condensed cloud of gases, containing mainly hydrogen and helium. A
protostar does not emit light.The
protostar is highly dense gaseous mass which continues to contract further
(shrink) due to gravitational force. As the protostar begins to contrast
further, the hydrogen atoms present in the gas cloud collide with one another
more frequently. These collisions raise the temperature of protostar more and
more. When the surface temperature becomes 1000K and inner core temperature
about 50000K particles accelerated towards the centre. But when the protostar
becomes 3 years old its surface temperature raise to 3000K and inner core
temperature around 150,000K. At this stage it becomes highly luminous and rate
of concentration decreases it requires 10 million years to reach the inner core
temperature to about 10,00,00,000K. At this extremely high temperature nuclear
fusion reaction of hydrogen takes place i.e. star was said to be born with its
own source of energy. The energy produced during this reaction makes the
protostar to glow and become a star.In
a star which is emitting light and energy two types of forces are acting
simultaneously. The gravitational force which trying to compress the gases and
the internal pressure due to nuclear energy trying to stop the gaseous matter
from collapsing. This balance can continue for millions of years. During all
this time, the nuclear fusion reaction continues to liberate energy and make
the star shine. Our sun is now in this balanced state of its development, was
formed about 4600 million years ago and will continue to give out energy for
equal period of time.

Initially proton-proton chain
reactions dominate and helium is formed. But at a later state when the inner
core temperature is around 10 million K, C-N cycle also contributes. Thus
slowly hydrogen is consumed to form helium by fusion reactions.1.     
Sequence Stars

The evolution of main
sequence stars depends on mass of the stars itself and it shall evolve in two

Low mass Stars (<8M_SUN)  In case of low mass stars, star will evolve to a Red giant phase & eventually the core of the star will make of carbon! So, outer atmosphere of the star becomes unstable and force of radiation from burning shells blows the atmosphere away-envelope ejected into the space. The ejected envelope expands into stellar medium forming a beautiful planetary nebula. The small, dead and dense core is nothing but a dead star, called White Dwarf.  The mass of it is 1.44M_Sun, which is known as Chandrasekhar Mass Limit. The small star Sirius B is a white Dwarf companion of the much larger and brighter Sirius A Star. Typical life cycle of sun is shown in the following figure. i.                    High Mass Stars (>8M_SUN)The massive stars can evolve further as they have
enough mass and the stars become hot to fuse carbon. Eventually the star ends
up with Iron core. As a result, no outward pressure, gravity wins and star
collapses rapidly. The result of the catastrophic collapse is the explosion of
the core, known as Supernova Explosion.
The core is another type of dead star.

the core mass is less than 3 M_SUN, the dead star is known as Neutron star and
if the mass is more than 3 M_SUN, it is called Black Hole.


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