Question: when stars collide is it likely it to form a black hole?

Sam Connolly answered on 17 Jun 2014:

Good question! Stars don’t collide very often, because there’s usually a
huge amount of space between them, so we haven’t actually seen it
happen, but it’s likely that in some situations it could form a black
hole, yes!

If two stars normal stars were to collide, the chances of getting a
black hole would depend on how big they are – you’d probably need two
stars which are a few times bigger than the Sun, or bigger. Even then,
they might not form a black hole straight away, because it might just
make a big star twice the size! It would eventually collapse into a
black hole after it has burnt all its fuel though.

You’re actually more likely to get a collision between stars if either
one or both of them aren’t normal stars though, but what’s left after a
normal star dies (if it’s not big enough to make a black hole on its
own). Stars often form in ‘binaries’, which is when you have two stars
orbiting around each other. They will get closer together over time, but
usually one, or both, dies and explodes before that happens, making
either a white dwarf or a neutron star, which are both very small, dense
objects which are heavy for their size. The death of one star speeds the process of them getting closer together. And because the objects are so dense to begin with, they’re far more likely to make a black hole when they do collide. In fact, we think that two neutron stars colliding and making a black hole might sometimes cause something called a ‘Gamma ray burst’, which is the biggest type of explosion we can see in space!