# How can we detect a black hole accurately?

I know there are many ways in detecting a black hole, but there are odds against them too. So I wanted to know a accurate method to detect a black hole.

Here are the known methods to me and the odds I think

One is by observing a dark region of space where even photon particles are missing and other is by detecting the X rays emitted from the black holes from our reference (say earth)

• If we decide to tell there is a black hole in a specific space by the absence of light, because black hole doesn't allow light to pass over them. The odd is that one can say that there is no nearby star producing enough light or can say that the light is not reaching the reference.
• If we decide to tell there is a black hole due to X rays emitted from it, one can say that the atmosphere in reference place is absorbing the X rays and not allowing them to get detected.

So is there any way other than these two to detect a black hole in space accurately?

• I don't understand your question. Watch a few of the videos at this UCLA site and then clarify for me what you are asking. I get that you want to know what an accurate method for detecting a black hole is, but I'm confused by the two bullet points you have there. It's not clear what they are meant to express
– Jim
Commented Jul 22, 2015 at 14:26
• @Jimself I think you can understand now after the edit. Commented Jul 22, 2015 at 14:33
• Neither of those things seem to be actual ways for detecting black holes. Check out the link I gave you. There's not much room for doubt that it shows a black hole. But we don't detect it because of an absence of light passing through or because of x-rays. The gravitational effect observed and centered on a dark body is what indicates it's a black hole. Also, the fact that there is no wobble of the central body at all as massive stars pass close to it indicates it's orders of magnitude more massive than any of the stars. Dark and way more massive than a star? Can't be anything but a black hole
– Jim
Commented Jul 22, 2015 at 14:44

One method is to measure the mass and radius of an object. For example we can measure the mass of the black hole at the centre of the Milky Way, Sagittarius A$^*$, by observing the orbits of stars around it. This works out to be about four million Solar masses. We can also estimate upper limits for the size of Sagittarius A$^*$. These upper limits are considerably greater than the Schwarzschild radius ($r_s$ is about 12 million km) but they are low enough that an object of that density must inevitably collapse into a black hole.