Astronomers have long wondered why it was that the super-massive black hole in the center of our galaxy was relatively quiet. Known as Sagittarius A*, a massive hole, containing about 4 million times the mass of our Sun. Yet, despite its size, the energy radiated from its surroundings is billions of times weaker than black holes at the core of other galaxies. Our neighboring galaxy, Andromeda, by comparision has a black hole 20 times the size of ours. However, the smaller size of the Milky Way and our distance from the galactic center (25,000 light years) may be a reason for our well-shielded existence. The fact that life exists on Earth, and the fact that we do not live on a planet closer to our galactic core, may not be a coincidence.
"We have wondered why the Milky Way’s black hole appears to be a slumbering giant," observed Tatsuya Inui of Kyoto University in Japan. "But we realize that the black hole was far more active in the past. Perhaps it’s just resting after a major outburst."
Tatsuya Inui was part of a team that used results from Japan’s Suzaku and ASCA X-ray satellites, NASA’sChandra X-ray Observatory, and the European Space Agency’s XMM-Newton X-ray Observatory, to determine the history of our black hole.
It turns out that, approximately 300 years ago, Sagittarius A* let loose, expelling a massive energy flare. Data taken from 1994 to 2005 revealed that clouds of gas near the central black hole, known as Sagittarius B2, brightened and faded quickly in X-ray light. The X-rays were emanating from just outside the black hole, created by the buildup of matter piling up outside the black hole, which subsequently heats up and expels X-rays.
These pulses of X-ray take 300 years to traverse the distance between Sagittarius A* and Sagittarius B2, so that when we witness something happening in the cloud, it is responding to something that happened 300 years ago.
Amazingly for us, in a rare occurrence of perfect cosmic timing, a region in Sagittarius B2, only 10 light-years across varied dramatically in brightness. "By observing how this cloud lit up and faded over 10 years, we could trace back the black hole’s activity 300 years ago," said Katsuji Koyama of Kyoto University.
"The black hole was a million times brighter three centuries ago. It must have unleashed an incredibly powerful flare."
The image at the top of the page shows the central region of our Milky Way Galaxy as seen by Chandra X-ray Observatory. The bright, point-like source at the center of the image was produced by a huge X-ray flare that occurred in the vicinity of the supermassive black hole at the center of our galaxy. Image: NASA/MIT/F. Baganoff et al.
Source: The Daily Galaxy via Kyoto University