The giant black hole in the Milky Way

Using the X-ray satellites of NASA, Japan and Europe, a group of Japanese astronomers discovered the central black hole of our galaxy that once emitted a very powerful energy fire 3 years ago. century.

This finding helps solve a long-standing mystery: why is the Milky Way's black hole so quiet? The black hole Sagittarius A * is actually a monster, having 4 million times the mass of the sun. But its source of radiation energy from its surroundings is billions of times weaker than the central black holes of other galaxies.

"We used to wonder why the Milky Way's black hole looked like a sleeping giant ," said Tatsuya Inui, head of research at Kyoto University, Japan . But we realize that black holes have been much more active in the past. Maybe he's resting after a boom. '

The new work will be published in the Publications of the Astronomical Society of Japan, combining results from ASCA and Suzaku Japanese X-ray satellites, NASA's Chandra X-ray Observatory, and X-ray Observatory XMM-Newton of the European Aerospace Agency.

Observations collected from 1994 to 2005 reveal that clouds of gas near the central black hole flare up and die quickly in X-rays as they respond to X-ray pulses emanating from just outside the black hole. When the gas spiraled into the black hole, it heated millions of degrees and emitted X-rays. The more matter accumulated near the black hole, the greater the X-ray source.

X-ray pulses take about 300 years to reach the distance between the central black hole and a large cloud symbolized Sagittarius B2, so the cloud records events that took place 300 years ago. When the X-ray flows to the cloud, they clash with iron molecules, knocking the electrons close to the molecular nucleus. When remote electrons fill this gap, the iron molecule emits X-rays. But after the X-ray pulses pass, the cloud fades away and returns to normal brightness.

Photo by Chandra captures the center of our Milky Way galaxy.The arrow indicates the location of the black hole Sagittarius A *, abbreviated Sgr A *.(Photo: NASA / CXC / MIT / Frederick K. Baganoff et al)

Surprisingly, an area within Sagittarius B2 only 10 light-years in diameter has a significantly different brightness in just 5 years. That change of light is also known as light echo. By analyzing the X-ray spectroscopy of iron, Suzaku's observations are important in eliminating the possibility of subatomic particles causing light echoes.

According to Katsuji Koyama, a member of Kyoto University, member of the research team 'By observing how the cloud is shining and decaying for more than 10 years, we can repeat the activity of the black hole 300 years ago. This black hole is a million times brighter than it was three centuries ago. He must have released an unbelievably powerful fire. '

This new work is based on research by many pioneering groups in the field of light wine. Last year, a group of scientists led by Michael Muno, now working at the California Institute of Technology Research in Pasadena, California, used X-ray bright observations of Chandra Observatory to prove that Sagittarius A * gave birth to a X-ray burst about 50 years ago - more than 10 years before astronomers could track X-rays in the universe by satellite. Muno said 'The explosion 300 years ago was brighter than what we discovered 10 times.'

The galaxy center is about 26,000 light-years from Earth, which means we can see events as they happened 26,000 years ago. Astronomers still lack the detailed knowledge of why Sagittarius A * has so much activity. Koyama said it was possible that a comet launched gas and swept into the black hole a few centuries ago, causing the black hole to "wake up" and produce a giant fire.

Launched into space in 2005, Suzaku is the fifth satellite in a series of satellites devoted to studying Japanese cosmic X-ray sources run by the Japanese Aerospace Exploration Agency (JAXA). This mission is a collaborative effort between Japanese universities and research institutes with NASA Goddard.