Question: What makes a black hole ?????

Linda Cremonesi answered on 17 Jun 2014:

A black hole is a usually defined as a point with infinite density and mass. This means that everything in black hole is all squeezed together and close to each other. A black hole will attract any object travelling close to it and nothing can escape from it (not even light!). The reason why it’s called black hole is exactly because we see a “black hole” in a particular fraction of space, because all the light is trapped in it and it looks black!

A black hole can be formed at the end of a star’s life. Not all stars will become black holes, only the very big ones. For example the sun is a small star (it’s called a white dwarf) and will not die forming a black hole, but would simply slowly “turn off”.

Bigger stars behave differently. So there are 2 opposite forces inside stars:
– on one side we have forces trying to make the star expand (making it bigger and bigger) thought nuclear reactions inside their core (these nuclear reactions are responsible for the light you see from the stars! That’s why they’re so bright!).
– on the other side the gravitational force (which is the same force that keep you attached to this planet) will try to make the star “shrink”.

These 2 forces battle continuously to stay in an equilibrium state, but after a long time the fuel for nuclear reactions runs out so we get a big explosion (a supernova explosion with lots of neutrinos generated) and the star will shrink into itself to become a very small point of infinite mass and density! And that’s your black hole 😀