There are about 100 billion stars in our galaxy. Imagine taking twenty percent of those stars and stuffing them into one, single black hole. That would be one hell of a black hole.Well, there is such a black hole, called OJ287 (no relation to the ex foot ball star/murderer). It is about 3.5 billion light years away.What is interesting about OJ287 is that there is so much gravity going on here …. between this massive black hole and a smaller black hole that orbits it … that you have to measure the orbital dynamics using Einsteinian calculations, which makes it a test of one of Einstein’s theories.(It turns out Einstein was right, as usual. What a brainy guy he was.)There are more details here.
Wow! It’s so big that it has a regular black hole in orbit? Crazy stuff, good thing it is far away.