They know because the effect the black hole has on other matter.
There has yet to be evidence that a black hole exists in M65.
A black hole is more dense. In principle, the black hole exists all at one point. So its volume is zero, and its density is infinite.
Not much actually. Scientists are still looking into it. What they do know though is that it has eaten up everything around it. Because of that, the supermassive black hole exists in a pitch black, empty area in the center of the Milky Way.
According to current theory, a black hole, if it exists, begins its life full,and nothing that falls into it ever leaves it.
No the singularity is at the core of the black hole.
Don't know which black hole.
Black Holes are space vacuum cleaner, it sucks everything into it; planets, stars, galaxy, even light. Black holes are invisible, but we know that it exists because it distort light and stars disappearing.
Because there is usually nothing around the spot where the black hole is because the black hole "ate" everything.
We know nothing about the conditions within a black hole, but it seems unlikely that a black hole could exist within a black hole, or even if this concept would have any meaning at all.
Nothinness, anything that even goes near a black hole is sucked in and ripped apart by the intence gravity until it no longer exists, this i suppose is why the center of a black whole is infintely small.
Never, because if we can thrive in it than we are not in a black hole
A black hole is formed and no temperature exists