What are black holes?
We can't see black holes
. That's because the gravity of these objects is extremely powerful. So powerful in fact, that not even light can escape from it.
Actually, anything that enters a black hole is trapped there and can never escape.
Escape velocity is the term scientists use when they talk about the speed a rocket must travel at to break free from the Earth's gravitational pull and enter outer space. The same term also applies to other objects in space.
Since we know that light can't escape from these objects, their escape velocity is greater than the speed of light.
How do we know where they are?
Scientists can detect these objects in outer space because they can see gas swirling around them at very high speeds. These swirling areas of gas cause hotspots in space. Areas of gas that are hotter than in normal conditions.
How many kinds are there?
There are 3 different kinds of these super-dense objects that we know about: