Q&A: Black Holes
How long does it take a star to form a black hole after its
Black Hole formation during the collapse of massive stars can
proceed in two different ways: either the massive star
collapses directly into a black hole without a supernova
explosion or an explosion occurs, but its energy is too low
to completely blow away the stellar envelope, and a
significant part of the star falls back to form a black hole.
In either case, calculations indicate that a black hole is
formed in a time that ranges from about a tenth of a second
to half a second!
An alternative path involves the collapse of a neutron star
into a black hole if it accretes so much material from a
nearby companion star, or merges with the companion star that
it is pushed over the neutron star limit and collapses to
become a black hole. This process could take a million years
or more depending on how quickly it accretes the material,
but once the neutron star is over the limit, which is about 3
solar masses, the collapse to a black hole occurs in less
than a second.