I like to read about black holes. I like to write about them, too—they’re fascinating. When I was a kid, black holes were one of those “weird cosmic things” that we’d read about in science fiction. In scientific circles, people considered them a theoretical possibility, but nobody had actually observed one. Turns out you really don’t observe a black hole. You look for the effect of the black hole on material (or space) around it. A black hole’s gravity warps space/time, which causes light to “bend” as it travels past, sort of like looking at a straw in a glass of water. That same gravity also sucks in nearby material, which coalesces into a wide disk of material called an “accretion disk”. The “stuff” in the disk gets funneled into the black hole, and on the way in it gets superheated. The highly hot material gives off radiation, and astronomers can spot THAT around the area of the black hole.
The black hole itself is a tightly compacted bundle of materials packed together so well and has a gravity so strong that nothing that gets inside it—not even light—can escape it. That’s the part about black holes I think fascinates us. What’s it LIKE in there? Nobody who goes in can ever tell you because they, and their messages, would never get out.
Black holes are a continuing source of study for astronomers. They find them all over the place, scattered throughout our galaxy. Most of them are stellar black holes, meaning they were created when old, massive stars died. However, at the center of our galaxy, there is at least one (and probably two) supermassive black holes.
It turns out that other galaxies have black holes. That makes sense. They have stars, including massive ones,l so when those stars die, depending on their masses, they too will make black holes. And, the centers of other galaxies have supermassive black holes, too. Astronomers are still figuring out how those behemoth black holes get into the central regions during a galaxy’s evolutionary history.
The Chandra X-Ray Observatory can easily spot the x-rays coming from regions around black holes in our galaxy and in others, too. Its data has revealed a large number of these cosmic zombies in the Andromeda Galaxy, our nearest spiral neighbor in space. Chandra has spied out 35 black hole candidates seemingly swarming around the center of the galaxy. Seven of those candidates lie dangerously near the core, about a thousand light-years away. Eight black hole candidates are associated with globular clusters, which is an interesting result. The Milky Way’s globulars have not, so far, shown us that they have any black holes.
Now, the interesting thing about Andromeda’s black holes is that in a few billion years, they’ll belong to the Milky Way. Or, to be more accurate, they’ll be part of a new galaxy that forms when the Milky Way and Andromeda merge. That process will begin in perhaps five billion years and take around 10 billion years to complete. At the end, there’ll be a massive elliptical galaxy containing the stars, black holes, and planets that used to exist in the two separate galaxies.
Want to read more about Andromeda’s newly found black holes? Check out the Chandra X-Ray Observatory Web page for details!