Sunday, April 12, 2015
A Monster Misses a Meal
There is a monster at the heart of our Milky Way Galaxy. It's a super-massive black hole that has already eaten enough material to make 4 million stars like our Sun! And, like all black holes, it is still hungry.
For material to be "eaten" by a black hole, it must come quite close to the black hole "mouth" which astronomers call its event horizon. Because black holes are the most compressed (squozen) objects in the universe, even overfed monster black holes have relatively small event horizons. Astronomers estimate that the one at the center of our Galaxy is 80 to 100 million miles across. That's roughly the distance between the Earth and the Sun and is a tiny space in which to put 4 million(!) Suns.
So material near our black holes must come close to that tiny region to serve as food for the monster. Things further away, like stars, can orbit around the black hole and not get swallowed. (It is from the movement of such close, but not doomed, stars that we can estimate the gravity of the black hole.)
For the last few years, astronomers who monitor the center of our Galaxy have been predicting that a snack is on its way to the black hole. A dusty cloud of material which they have nicknamed G2 was going to have a close encounter of the worst kind with the black hole in May 2014. It was going to be torn apart by the enormous gravity of the monster and some of its material was then going to provide a meal for the black hole.
When gas clouds (or other food) fall into a black hole, they are whirled around with unbelievable speed just before they fall in, and tend to glow briefly with x-rays and other forms of radiation before they disappear in the event horizon. However, no such flare-up of radiation was seen, even when the world's largest telescopes (like the Keck in Hawaii and the European Very Large Telescope in Chile).
It appears G2 was not torn apart and consumed, because it wasn't a loose cloud of raw material, but a star with some of its birth material still around it. The star managed to hold on to its "stuff" and make it away from the black hole, depriving it of a meal at this time. Sorry, monster. Better luck next time.
(In the picture, you see G2 in different colors going around the black hole (which is invisible, but whose position is marked by the plus sign.) The blobs are shown at different times, and are red when G2 was moving away from us, and blue now that it was flung around the black hole and is coming toward us.)