What happens if the core of a star exceeds the maximum possible mass for a stable neutron star?
Calculations, and many indirect observations, suggest that there is no force in nature that can
stop its gravitational collapse. As the core collapses the gravitational field builds up rapidly and at
some point becomes so strong that the star essentially digs a hole in spacetime
and falls into it.
For this truly bizarre object the escape velocity exceeds even the speed of light:
it has become
a black hole.