When a star with a mass more than 20 times that of the Sun
explodes as a supernova, it may leave behind a core so massive that even a
neutron star is not its final state. The object's gravity may be so great that
it goes on collapsing for ever, crushing the matter within it to an
unimaginable state. As the object's density gets greater and greater, the force
of gravity rises even more until nothing can escape — not even light. The
object has become a 'black hole'. At the centre of the black — hole, the
remains of the former star would be crushed to infinite density. in zero
volume.
Alifye - Space and Astronomy - Black Holes |
Black holes are invisible because they emit no light. However, objects
can fall into a black hole, when they cross its‘ gravitational boundary. Once
inside they can never escape. A black hole twice the Sun's mass makes a
gravitational well 13 km. in diameter in space.
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