How do scientists know that black holes exist if these objeccts don't emit any visible light?

Answer 1

By the radiation from matter falling into the black hole. The exact pattern of the radiation shows the matter is falling into a black hole. You can't match that any other way. Details:

http://curious.astro.cornell.edu/question.php?number=50

Answer 2

So many Top Contributors, so many wrong answers. The answer is YES,and Yes, light (or electromagnetic radiation), cannot escape a black hole, but that does not mean they are black, that only means light is not escaping (for the next trillion trillion years at least). They are in fact visible. As an object falls, you for example, into a black hole you would appears to an outside observer to slow down, infinitely slow to the point where your image and all the bits of information that made you up is spread across the surface (schwarzchild or event horizon) at the rate of 1 square planck's length per bit. I can see on the event horizon 's surface EVERYTHING that has ever fallen into the black hole.

Answer 3

Not just light. They don't emit any radiation in the electromagnetic spectrum. However, just because you can't see something, doesn't mean you can't tell it's there. Imagine a bath full of water. If I pull the plug out, you will see the water start to circle, and disappear. You don't have to be able to see the plug hole in order to figure out that there's a hole there, and it's swallowing everything in its vicinity.
Scientists observe gravitational effects going on in space, and theorize about a body that might cause these effects. The name they give to that body is a black hole. If similar effects occur somewhere else in space, the term they use is again 'black hole'. They are describing the effects that are going on, not an object that they can see directly.

Answer 4

You said it, they don't reflect light (not emit) as they absorb all the light.

HOWEVER.....

As these objects have a big gravitation force, the gas around them (particles) spins faster and faster until they heat up due to friction. Hence;

1. They emit IRs
2. They emit UVs

Thus, they can be detected by searching for IR or UV sources
known in the past to be a star the went into a supernova.

Answer 5

Black Holes emit many different kinds of radio signals. Yes, Black Holes do not emit light, but I'm sure astronomers use some kind of special meter to find them.

Answer 6

Much of the reason that lead them to look for their existence is complex mathematics that predict that they would. Then they looked for phenomena that would show if they existed or not.

There are various things such as x-ray "plumes" that emit from the axis and other forms of radiation that occur before at the event horizon. These can be observed.

Answer 7

They do not know for certain. Direct observation is not possible. Black holes are theoretical speculation based on the observed gravitational effects on other objects in areas of space where they are thought to exist. They do radiate energy in different forms (cf. Stephen Hawking).

Answer 8

By the effect of things around them. A black hole bends light, So while things directly behind it are blocked. Things around its hidden edge show back up before they would if the light did not bend.

Answer 9

Black holes emit a huge gravity , which keeps all the solar systems in orbit. It is so large that it may be 100 light years across.

Answer 10

Their tremendous gravitational forces bend and distort light and other waves/particles from adjacent stars. There is also the obvious emptiness when a black hole eclipses background luminaries.