Stars Becomes Black Holes

By Sarah  2019 batch 

A black hole is defined by the escape velocity that would have to be attained to escape from the gravitational pull exerted upon an object. A black hole itself is invisible because no light can escape from it. When black holes were first hypothesized they were called “invisible stars”. 

A common type of black hole is the type produced by some dying stars. A star with a mass greater than 20 times the mass of our Sun may produce a black hole at the end of its life. In the normal life of a star there is a constant tug of war between gravity pulling in and pressure pushing out. Nuclear reactions in the core of the star produce enough energy to push outward. For most of a star’s life, gravity and pressure balance each other exactly, and so the star is stable. Howerver, when a star runs out of nuclear fuel, gravity gets the upper hand and material in the core is compressed even futher. The more massive the core of the star, the greater the force of gravity that compress the material,collapsing it under its own weight. When a less massive star exhausts its nuclear fuel it cools and dies peacefully whereas very massive star exhausts it nuclear fuel it explodes as a supernova. The outer parts of the star are expelled violently into space,while the core completely collapses under its own weight. 

According to theory, there might be three types of black holes: stellar, supermassive,and miniature black holes depending on their size. These black holes have also formed in different ways. Stellar black holes are formed by the gravitational collapse of a star. Supermassive black holes likely exist in the centers of most galaxies,including our own galaxy, the Milky way. In the central region stars are tightly packed and black hole in the center of a galaxy can become more and more massive as stars orbiting the event horizon can ultimately be captured by gravitational attraction and add their mass to the black hole. Miniature black holes in theory might have formed in the early universe but astronomers do not have any evidence of their existence. .Miniature black holes have even horizons as small as the width of an atomic particle and might have been created during the Big Bang.