What is a supermassive black hole?
I know I've talked about this before, but I believe that I should discuss what these really are. No, this isn't about the group Muse; although the line 'And the superstars sucked into the supper massive' could apply here.
I've already discussed black holes, but these supermassive black holes are in a class by themselves. They have masses that blow our minds, hundreds of billions of suns. The first thing that's wild about these black holes is that their densities are less than that of water. Wait, how is that possible? The answer is that they have large volumes. This is the result of the so-called Schwarzschild radius, which is when all of the mass inside the radius of a massive object causes the escape velocity at its surface to be the speed of light. This Schwarzschild radius is proportional to mass and density, and is inversely proportional to volume. If you do the math a supermassive black hole has a relatively low density. The bottom line is that you have to go deeper into a supermassive black hole before you would be torn to shreds, not that anyone is going to test this theory.
So, what's so important about these supermassive black holes? The answer is that every galaxy, including ours, has one of these beasts at its center. Cosmologists believe that they are the reason for galaxy formation. In other words, we wouldn't be here if it weren't for supermassive black holes. However, there is a lot of disarmament about how they were formed. The problem lies in the fact that for a black hole to get so massive it would have to eat a lot of stuff, and this stuff would have to be not spinning around the black hole in an accretion disc because it has to fall in, not spin around. What are missing are black holes between those that form from the collapse of a giant star and those that reside in the center of galaxies. This is a lot like evolution where we don't find the intermediate species. The only way that these supermassive black holes could form is that they did so after the formation of the first super large stars, which burned out and collapsed fairly early on. Then, these large black holes had to find each other and merge to form the really supermassive black holes we see now in the center of our galaxy.
How do astronomers know that there's a supermassive black hole in the center of our galaxy? They know this by observing the movement of stars close to it. The center of our galaxy is called Sagittarius A. This is a radio source that is believed to be the result of action near the event horizon of the supermassive black hole. By observing the movement of stars orbiting close to the center, astronomers were able to calculate the mass and size of the alleged supermassive black hole. Normally, telescopes can't penetrate the clouds of gas and dust near the center of the galaxy, but by using infrared light, the stars can be seen and their motions plotted. Knowing the mass of the stars and their motions allows astrophysicists to calculate the mass and volume of what they're orbiting.
Another sign that there is a supermassive black hole at Sagittarius A is the discovery of a gas cloud using X-ray telescopes. This gas cloud that's about three times the mass of Earth is swirling around and into the accretion disc of the supermassive black hole. This and other observations of clouds of dust and gas being sucked into the black hole proves that the Milky Way's supermassive black hole is starting to get active again and may be working up to forming a quasar, but it won't do this for millions of years.
Thanks for reading.