Anand7sem

Hi all, I need a help to find the answer of following. As per Wikipedia and other sources Black hole is created after death of a Star. As per them when such a huge mass of supernova remnant collapses on itself and the small point(core) create an extremely strong gravitational field due to the huge mass got captured in a small point. But I can't understand what is the relationship of "volume" of the remnant to gravitational field ? When same mass(or greater) was a size of red Giant then there wasn't such a strong gravitational field there. But when the volume got smaller then how the Gravitational field got stronger ?? Thanks in Advance