Black Holes : Mysteries

Journalism contest 2001 entry second prize in IIT Bombay

Black holes..... The most tragic eventual end of the life of any star ! Let us know how it actually happens !The life cycle of a star starts when a large amount of gas, mostly hydrogen starts to collapse into itself due to gravity!The atoms of hydrogen start colliding with each other resulting into heating of the gas and the heating then becomes enough for the hydrogen to start coalescing to form helium.The heat not only raises the temperature but also the pressure of the gas which helps it sustain itself from its own gravity.Stars tend to remain stable like that until their fuel is almost exhausted.The stars too face the fuel crisis!And then they have no option but to contract under their own gravity.

Chandrashekhar found out that when the star becomes very small the part icles (electrons) start getting closer to each other and Pauli's exclusion principle says that they should approach each other with different velocities. And this makes the star to expand.It is this thing that can save the star. But then there comes a limit to the repulsion that can be provided!The maximum difference between of velocities of the particles is limited by relativity to the speed of light and this suggested that there will be a time when the star would be so dense that the gravity would overcome the repulsion and this results that a cold star of mass about one and a half times that of the sun won't be able to support its gravitational attraction and collapse. And if the mass was less than the now called "Chandrashekhar's Limit" then it would exist in that state.The state called the white dwarf state.

But what if a star has a mass of greater than the limit ?May be it would explode and throw off enough matter to reduce below the limit to avoid this disaster!But then the question comes how will the star ever know that I have got on much weight and I have to reduce it ?And if ever this happened what if some mass was added to it ?Will it start repelling it ?Or would it prefer falling into a condition of infinite density ? General relativity provides the answer .The gravitational field yields the spacetime a curvature leading to bending of light rays so that they follow geodesics.This is confirmed from the observations of the bending of light rays near the sun verified during eclipses! Now say the star shrinks to so much that light is not able to escape then nothing would escape from the gravity of this star now termed as being a "BLACK HOLE".

And then comes the obvious question of how to detect the black holes if they do exist ! But fortunately there is a way out for though the black holes are "black", their gravitational power is still strong to produce strong effects.There are stars which seem to go around noone It is possible that the other stars are too faint to detect .But is also seen that the systems are a good source of X-rays.One explanation goes this way!The star which revolves will get teared off due to the gravitational tide caused due to difference in the force of gravity at two distant points which would lead to the tearing! This falling matter heats up and then causes the X-rays to be emitted.Such systems include the Cygnus X-1!

There are evidences of black holes existing in other parts. Also is possible that the universe is full of black holes and these with the help of Dark Matter does explain the various phenomenon that are seen and can't be explained with the predicted visible mass of the universe!

And to conclude..

We're going through the time of constantly newer and better theories. We hope to reach the ultimate truths and fate of our Umiverse in near future.