Lifecycle of A Star
Lifecycle of A Star
Stars are such astronomical bodies
which spontaneously emits light and heat. There is 70% Hydrogen, 28% Helium,
1.5% Carbon and 0.5% Neon and Nitrogen in a star. We can classify stars by
their colours, size and brightness. Generally, there are three colours of stars-
red white and blue. Colours show the temperature of a star. White colour shows
a high temperature while the blue colour shows a high temperature of a star.
Origin of a Protostar: The life of a star starts in galaxy by condensation of
Hydrogen and Helium. This gas transforms in cloud which have temperature of
about -1730C. As these clouds become greater, their gravity becomes
higher. When the size the size of a cloud becomes high enough, it stars contract
itself. This body is called a protostar which does not emits light.
Formation of a Star
from Protostar: Protostar is very
dense body which continues contracting because of high gravity. In this
continuous process, the hydrogen atoms of protostar collide with each other. So
the temperature increases itself. This process continues for almost lakhs of
years. Temperature of the star gets higher and reaches at 107 oC
during this process. The fusion reactions of Hydrogen take place at this
temperature. Helium atoms are made from these reactions. High energy is also
produced with Helium which makes the tar bright.
Final stages of a star’s
life-
Red-Giant Phase: When whole Hydrogen in crode is transformed in Helium
by fusion. The pressure in crode becomes much less and the star starts
contracting under its own gravity. Yet some hydrogen is left in outer layer of
star which starts reactions and emits light. But this emission of light is too
slow. The outer layer of star starts expanding and the crode starts contracting
for balance. This state of star is called Red-Giant star. The red-giant star is
an unstable state. Our sun will change into red-giant star after about 5000
million years.
If a start’s mass is less than the
Chandrashekhar limit [1.44 times of mass of the sun], it will eventually stop
contracting and settle down in a stable final state as a ‘white dwarf’ with a
radius of few thousand miles and density of hundred tons per cubic inch. A white
dwarf is supported by the exclusion principle between the electrons in its
matter. We have observed a large number of these white dwarf stars. One of the
first to be discovered is a star that is orbiting around Cirius (The brightest
star in the sky).
A scientist, Landau pointed out
another possible final state for a star, also with limiting mass of about one
or two times the mass of the sun but much smaller even than a white dwarf. These
stars would be supported by the exclusion principle repulsion between neutrons
and protons, rather between electrons. They are therefore called neutron stars.
They would have a radius of only 10 miles and density of hundred million tons
per cubic inch. At the time they were first predicted, there was no way that
neutron star could be observed. They were not actually detected until much
later.
Black Holes: The fate of neutron star depends on its mass. According
to the scientists, the contraction of neutron stars takes place for infinite
time which eventually converts into black hole. Black holes have infinite
gravity. Even light can’t come out of the black hole. So, none can see it. We can
only notice its effect on nearly bodies.
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