Neutron Star Black Hole (Nandan Nayak)

The birth, life and death of a star is determined by interplay of nuclear reactions and the gravitational forces. The nuclear reactions that take place in the interior of the star will create a radiation pressure which in turn tries to push the star outward. However the gravitational forces between the particles of the star will try to pull it inward towards the center.When there is a balance between the outward radiation pressure and the inward gravitational pressure the star attains stability. However, when the nuclear fuel inside the core of a massive star gets exhausted, the star collapses under its own enormous gravitational force., As a result the star shrinks to a smallest size. This collapsed star will be so dense that even light cannot escape from it. Such an entity in the cosmos is called 'Black hole'

Introduction to Neutron Star Black Hole

A star is formed when a large amount of interstellar gas, mostly H2 and He starts to collapse on itself due to the gravitational attraction between the gas atoms or molecules . As the gas contracts it heats up due to atomic collisions. As the gas continues to contract, the collision rate increases to such an extent, that the gas becomes very hot, and the gas atoms are stripped off their electrons, and the matter is in a completely ionized state, containing bare nuclei and electrons. Such a state of matter is called plasma state. Under these conditions, the bare nuclei have enough energy to fuse with each other. Thus hydrogen nuclei fuse in such a manner to form helium with the release of large amount of energy in the form of radiation. The radiation emitted in this process is mostly emitted in the form of visible light, UV light, IR light etc., from its outer surface. This radiation is what causes the star to shine, which makes them visible (Ex : Sun and other visible stars).

Neutron star black hole : Process

The star at the stage is halted from gravitational collapse( contraction) since the gravitational attraction of matter towards the centre of the star is balanced by the out ward radiation pressure. A star will remain stable like this for millions of years, until it runs out of nuclear fuel such as H_ and He. The more massive a star is , faster will be the rate at which it will use its fuel because greater energy is required to balance the greater gravitational attraction owing to greater mass i.e., massive stars burn out quickly. When the nuclear fuel is over, i.e., when the star cools off, the radiation pressure is not sufficient to halt the gravitational collapse. The star then begins to shrink with tremendous increase in the density. The star eventually settles into a white dwarf, Neutron star or Black hole depending upon its initial mass

Neutron Star and Black Hole : Conditions

For a star to become a neutron star, its initial mass must be greater than ten solar masses. (M> 10Ms ). As a star with initial mass M > 10 Ms cools off the large mass of the star causes it to contract abruptly, and when it runs out of fuel it springs back and explodes violently. This explosion flings most of the star matter into space and such a state of star is called a Supernova. A supernova explosion is very bright and outshines the light of an entire galaxy. The mass of the matter left behind is greater than 1.4 Ms . If the mass of the left over matter is between 1.4 Ms and 3 Ms Neutron stars evolve. At this stage the repulsion between electrons will not be able to halt further gravitational collapse. Under such conditions, the protons and electrons present in the star combine to form neutrons. After the formation of neutrons, the outward degeneracy pressure between neutrons prevents further gravitational collapse, and the matter left over is called the Neutron Star.

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