It wasn’t until more recently that scientists even knew that black holes existed. One of the main reasons is, black holes are so black, that they can’t be seen, even with the most powerful equipment. While Einstein made the prediction that there were black holes, it wasn’t until 1967 when the name ‘black hole’ was created and then it was discovered that there is a massive black hole in just about every large galaxy.
It’s kind of difficult to see something like a black hole, but we need to see it to study it. The universe gives us a little help, because while we might not see the black hole, we can see the light from everything that it is consuming.
Scientists think that they are created when a massive star dies in a supernova explosion and its gravity is so great that it crushes in on itself with such strength that it overpowers all other forces. It develops such an intense gravitational pull that not even light can escape it. It continues to pull everything in its path into itself. They call that process ‘feeding a black hole’.
Since there are so many stars that have died as supernovas, it’s thought that there are millions, possibly billions of them in the universe. The power of the black hole is greater than anything else that has been found so far, and scientists believe that this massive gravity slowly pulls at the materials that galaxies are made of during their creation.
As material is pulled closer to a black hole, some of it is consumed, but other parts are just out of reach of the gravity. It’s thought that the gravity of the black hole starts the new galaxy to begin spinning. All suns and planets that are ‘out of reach’ of the black hole continue to spin around it. Anything that gets too close, will be quickly ‘eaten’.
The only way scientists can observe them is by watching what happens when anything gets too close. This can be dust clouds, planets or even stars. As the object gets close, it is slowly pulled apart and gives off x-rays that we can measure. In some cases, a gas cloud can be lit by the light of the sun and we can actually ‘see’ the black hole in the center, because it’s the only thing that is totally black.
Black holes are only active when they have something to eat. If there isn’t anything close enough, they go into what is called a ‘dormant’ cycle. They are still dangerous, and will quickly become active again if something comes close enough.
They are believed to be at the center of every galaxy because they have such gravitational power and strength that they can pull the rest of the dust, asteroids, planets and suns close to it. Anything that was around during the explosion of the star that went supernova will be pulled into the gravity and spin of the black hole. Everything that is just far enough away will form the galaxy, the rest is dinner for the black hole.
Nasa Website - Black Holes
NASA videos on black holes - lots to choose from