A stellar mass black hole is around 10 solar masses, and some stars can be much massive than this. And doesn't a black hole have more gravity than anything in the universe? Does more mass necessarily mean more gravity? If a star is more massive, how can a black hole siphon off material from it? Does this just have to do with size? b/c I remember seeing white dwarfs siphoning material from their giant companion stars. I know in a binary system stars orbit each other, but what happens after one becomes a black hole? do they continue to orbit each other? Also, what causes some black holes to rotate and others not to? Why do black holes that do not rotate have double the diameter of black holes at the theoretical maximum?