One Universe at a Time

In the center of our Milky Way galaxy is a supermassive black hole. We can’t see this black hole directly because there is too much dust in the direction of galactic center, but radio waves can penetrate that dust, so we can observe the radio signals of hot stars and gas near galactic center. We’ve been observing these signals over several years, and we’ve noticed how the stars near galactic center orbit the region very quickly. From their orbital motion and a simple use of Kepler’s laws we can get a pretty good idea of the mass of the black hole. It turns out to be about 4 million solar masses. While this is a huge black hole, most of the stars orbiting it aren’t too terribly close. So for the time being they aren’t at risk of being ripped apart by the intense forces near the black hole. But there was one object recently that did make a very close approach.