What is Sagittarius A*?
Sagittarius A* (pronounced “A-star”) is a region in the center of our galaxy, approximately as wide as the orbit of Pluto, containing 3.7 million solar masses of material. Located near the galactic center, Sagittarius A* is suspected by astronomers to be a supermassive black hole, serving as the center of gravity for the entire galaxy. Sagittarius A* is closely orbited by at least a dozen stars, the trajectories of which have been used to estimate its mass. It may even be orbited by the first observed intermediate-mass black hole, GCIRS 13E, which is estimated at 1,300 solar masses. As the mass of a black hole increases, the radius of its event horizon increases at a linear rate, but the density decreases as the cube of the radius. So, while black holes like Sagittarius A* are very massive, when you count the huge area of the event horizon, estimated at 6.25 light-hours (45 AU) or about 4.2 billion miles, the average density of the hole is no greater than that of air! Stellar-mass blac
