Detecting Black Holes

Factual Questions
1

What are all the ways that black holes can be detected?

2
  1. It can act like a lens making the objects behind it warped.
  2. We can look at objects orbiting it, calculate it’s mass and not that no known object can be that small yet have such a large mass
  3. We can detect x-rays eminating from the super hot material orbiting it.
    … There may be more
3

I’ll rewrite two since it has an typo and is uncomprehensible with it.

  1. We can look at objects orbiting it notice how quickly it revolves around the central object. Calculate the mass of the central object and note that no known object can be that small yet have such a large mass