Question
My students are very curious about black holes. Is there an active black hole in the center of our Milky Way Galaxy? How do we know?
Answer
There is a black hole in the center of our Milky Way Galaxy, but it's not very active. Astronomers have used the Keck observatory in Hawaii to measure the movements of stars very close to the center of our Galaxy. They found that the orbits of the stars around the Galactic Center show that the central mass is about 3 million times the mass of our Sun. The only object we know of that could have so much mass in such a small volume without emitting much more light than we see there is a black hole. Other astronomers have used the Chandra X-ray satellite to look for high energy events from around the black hole. They found a few X-ray flares, but these were relatively weak, suggesting that there's not much gas falling into the black hole at the moment. Astronomers think that the supermassive black hole at the center of the Galaxy has been much more active in the past.
http://chandra.harvard.edu/photo/2003/0203long/index.html
Black Holes, Center of the Milky Way Galaxy
http://vrd.askvrd.org/services/answerschema.xml
