Sgr A* Is a Hungry Black Hole

Chandra X-Ray Observatory Uncovers its Eating Habits

Our galaxy has a hungry supermassive black hole at its heart. It devours anything that happens to fall its way. Astronomers know that it has eaten a couple of times in the past few centuries and it’s doing it again right now. By studying x-ray emissions given off as the black hole eats, and measuring those emissions as they bounce off nearby clouds, astronomers can trace the eating habits of Sagittarius A* (the black hole’s name; Sag A* for short).

Over the past 12 years, astronomers using NASA’s Chandra X-ray Observatory have studied the central area of the Milky Way around the black hole. The data they took contains evidence that the normally dim region very close to Sgr A* has flared up with at least two very bright outbursts in the past few hundred years.

The astronomers watched rapid variations in the x-ray emission from gas clouds surrounding Sgr A*. So, how were the light-echoes produced? Astronomers suggest that they came about when when large clumps of material, possibly from a disrupted star or planet, fell into the black hole. Some of the x-rays then bounced off gas clouds about 30-100 light-years away from the black hole. Just as echoes of sound reverberate long after a noise is created, light echoes in space replay the original event.

While light echoes from Sgr A* have been seen before in x-rays by Chandra and other observatories, this is the first time that evidence for two distinct flares has been seen within a single set of data. The light echoes suggest that the area very close to Sgr A* was at least a million times brighter within the past few hundred years. X-rays from the outbursts (as viewed in Earth’s time frame) that followed a straight path would have arrived at Earth at that time. However, the reflected x-rays in the light echoes took a longer path as they bounced off the gas clouds and only reached Chandra in the last few years. This is how scientists know that Sgr A* has been snarfing down material that falls its way. And, it doesn’t do it quietly. Producing x-rays implies a tremendous amount of energy is released each time the black hole gobbles up material.

If you want to know more about how the astronomers studied these emissions, check out the full story on the Chandra web pages. And, stay tuned. Astronomers are tracking an other cloud of gas and dust that is headed for Sgr A*. It is arriving about now, and will take about a year to be fully assimilated into the collective that is Sgr A*. Observatories are geared up to watch the region around the black hole light up as this three-solar-mass cloud of material heads into oblivion.