Binary Black Holes

[BAZ]

We find one pair, now they are all over the place like a rash. 

 

http://www.iflscience.com/space/a-pair-of-giant-black-holes-has-been-spotted-photobombing-the-andromeda-galaxy/

[+Graham]

Here is an interesting question.

What happens if two black holes collide.

Would they cancel each other out or would it be the old

'irresistible force' meeting the  'immovable object'  paradox

[BAZ]

They merge, creating an even larger singularity, but in doing so release huge amounts of energy. They have detected six black hole mergers with LIGO to date, they are capable of working out the size of the two original components and the resulting merger mass. They suspect that this is how super massive black holes form.

There are some absolute monsters out there, the Lenticular galaxy NGC1277 is unfortunately famous for having a super massive black hole at it's core which is estimated to be around 6 billion solar masses, approximately  14% of the the entire galaxy's mass. I am guessing that wouldn't be a fun place to live.