As a kid, I used to look up to the sky and try to count the number of stars. But I wasn’t as intrigued by what happened inside of them till I heard the story of black holes. For the first time, I was super intrigued by these seemingly super mysterious points in our universe. What are they? How are they made? What happens inside of them?

While the question of what happens inside of them might be the subject of another upcoming post, if scientists manage to crack that code, I did manage to learn about how they are theoretically predicted as well as experimentally formed. Lo and behold, stars had a lot to do with it!

In Einstein’s General Relativity, we can write down the Einstein’s equations and calculate the solutions to these equations. A particular class of solutions which are called as Vacuum Solutions, exist, among which the “Schwarzschild Solution” is a special one. This is a metric which describes the space-time around a spherically symmetrical mass in the universe and it looks like this:

If we calculate the poles of this equation, we find that the equation predicts an event horizon as well as a singularity! If a star many times the mass of the sun goes through the whole chain of nuclear fusion events and ends up quite heavy, it would at some point collapse under its own weight and would form a blackhole if it is trapped inside it’s own event horizon! At this point, the mass and gravitational force of this star becomes so high that not even light can escape the confines of the event horizon! And thus, we do not have a direct probe for the inside of this hole due to which it looks black to us!

And thus, it is a black hole!! And to top this post off, here is a picture of a blackhole swallowing a star!