They are invisible.
You can't use spectrometers to detect black holes. Telescopes are the only way to detect them.
Astronomers use evidence such as the behavior of nearby stars and gas, as well as the bending of light around invisible objects, to detect the presence of black holes in space.
It is not known how many black holes exist. One of the main reasons is that, if matter is not actually falling into the black hole, it is impossible to detect.
I am not entirely sure what the question is. Anyway, black holes cannot be seen directly. You can detect their presence due to their gravitation.
They use X-Rays from the stars being sucked into them.
Black holes do exist - they are just VERY difficult to detect.
Black holes are a bit hard to detect, so I am pretty sure that not all black holes in this galaxy are known - and I suspect there is not even a decent estimate. But you can expect there to be several.
Scientists can detect black holes by using x-rays and gamma rays. Black holes still can release matter, and black holes give off a lot off x and gamma rays.
The nearest know black hole is at a distance of several thousand light-years. There are probably black holes closer by, but they are hard to detect, if they don't happen to be part of a close binary star system.The nearest know black hole is at a distance of several thousand light-years. There are probably black holes closer by, but they are hard to detect, if they don't happen to be part of a close binary star system.The nearest know black hole is at a distance of several thousand light-years. There are probably black holes closer by, but they are hard to detect, if they don't happen to be part of a close binary star system.The nearest know black hole is at a distance of several thousand light-years. There are probably black holes closer by, but they are hard to detect, if they don't happen to be part of a close binary star system.
The whole idea of black holes is that nothing, not even light, can escape from them. However, there are several indirect ways to detect them.
Currently we are unable to view black holes directly. We can only detect them indirectly by their effects on the movement of nearby objects and by X-rays emitted from superheated matter falling into them.
Most of the methods to detect black holes rely on their gravitational effects. The following are ways in which black holes can be detected, at least in theory:Hawking radiation: This radiation would be way too weak to detect a stellar black hole, but it might be used to detect primordial black holes. This method hasn't been successfully applied yet; perhaps there are no primordial black holes.A black hole's gravitational effect on a neighboring object; for example, stars orbiting Sag A* make it possible not only to conclude that there is probably a black hole there, but also to estimate its mass (current estimate: about 4.3 million solar masses).Matter falling into the black hole will emit strong x-rays.An accretion disk around a black hole will heat up through friction, and also emit radiation.Gravitational lensing of objects behind the black hole also make it possible to detect a black hole in some cases (when there is a good alignment).