Are black holes detected by the X-rays they emit?

It is possible to detect black holes by the X-rays emitted at the event horizon. That's one way to "see" them. It's tricky, but the tools of the modern astronomer are nothing short of astonishing. Let's take a walk.

Lots of times we think of telescopes as instruments through which bleery-eyed investigators peer for hours on end. It ain't like that now. In addition to the optical telescopes we know of (which now have CCD imaging equipment at the focal point and computers to look at the pictures), we have "eyes" pointed at the sky that can see across the electromagnetic spectrum, including X-rays.

The X-rays generated at the event horizon of a black hole appear as the result of the acceleration of gases into the gravity well. And we have things like the Chandra X-ray Observatory to see such things. Chandra launched in the summer of '99, and by the 2000's, stunning images were beginning to amaze observers. Including things like X-ray emission from Sagittarius A's supermassive black hole, which is at the center of the Milky Way.