What is Sagittarius A*, exactly?
Well, we can say what it isn’t: • It’s not a star. • It’s not a pulsar. • It’s not a supernova remnant. The properties of Sagittarius A* are consistent with the hypothesis that Sagittarius A* is an accretion disk around a supermassive black hole. Additional support for the hypothesis that Sagittarius A* harbors a massive black hole comes from the recent discovery that Sagittarius A* is also a potent source of X-rays. Only very hot gas emits X-rays (for instance, gas that is being compressed as it falls toward a black hole…
