It packs 4 million times more material than our sun, but relative to the black holes sitting at the center of some neighboring galaxies, it actually doesn't do all that much. The fact that this black hole, known as Sagittarius A*, kicks out billions of times less energy than others of its kind has made it something of a mystery. But now a team of scientists at Kyoto University suggests that Sagittarius A* may be resting after a far more active period a few centuries ago.