There is a monster at the center of our galaxy: A black hole, known as Sagittarius A*, weighing 4.3 million times as the sun and measuring about 25 million kilometers (15 million miles) across. At present the monster is slumbering, betraying its presence only by a slight snore of radiation, but it was not always so calm. A new study using the Chandra X-ray Observatory has picked up echoes of past outbursts within the past few hundred years--moments when Sagittarius A* was wide awake, blazing a million times as brightly as it does today.
Sagittarius A* -- the giant black hole at the center of our galaxy -- appears dim in this composite image because very little material is falling into it. (Credit: NASA/UMass/D.Wang et al; NASA/STScI) The idea that a black hole can be bright seems paradoxical at first. In reality, the emission comes not from Sagittarius A* itself ...
