One of the key differences between galaxies with super massive black holes is whether or not the black holes are lit up, because they are basically bingeing on a lot of material in its surroundings.
The question that I started off with was, I thought, very simple. It was just 'Is there a massive black hole at the center of the Milky Way?' But one of the things I love about science is that you always end up with new questions.
An ordinary black hole is thought to be the end state of a really massive star's life.
Black holes are very exotic objects. Technically, a black hole puts a huge amount of mass inside of zero volume. So our understanding of the center of black holes doesn't make sense, which is a big clue to physicists that we don't have our physics quite right.
One of the big mysteries about the black hole at the center of the galaxy is, 'Why don't we see emission from matter falling onto the black hole, or, rather, the black hole eating up its surroundings?'
Our galaxy's pretty ordinary, garden-variety. So if we believe our galaxy has a super massive black hole, that tells us that most, if not all, galaxies host such a black hole at their centers.
As an astronomer, I get to ignore the details of the things that we don't understand. There's a lot of work that we can do on scales that we do understand, and there is actually a finite size that I can associate with a super massive black hole.
We have this interesting problem with black holes. What is a black hole? It is a region of space where you have mass that's confined to zero volume, which means that the density is infinitely large, which means we have no way of describing, really, what a black hole is!
The key to proving that there's a black hole is showing that there's a tremendous amount of mass in a very small volume. And you can do that with the motions of stars.
'Black Hole Sun' was written in a car when I was driving home from the studio one night. Pretty much everything that you hear was written in my head.
