A dusty red object at the heart of our Milky Way Galaxy called G2 is a pair of binary stars that merged together, according to a team of researchers led by Dr Gunther Witzel from the University of California Los Angeles.
This image shows the supermassive black hole Sgr A* and the region around it. The inset shows Sgr A* and G2. Image credit: NASA / CXC / MIT / F.K. Baganoff et al. / E. Slawik / G. Witzel et al.
Since 2002, astronomers have been puzzled by a bizarre object at the Milky Way’s center that was believed to be a gas cloud headed toward our galaxy’s supermassive black hole, called Sagittarius A* (or Sgr A* for short).
The object, G2, lies about 26,000 light-years from our Sun and has a mass about three times that of the Earth.
It has been observed to be disrupting since 2009, and was predicted by some astronomers to be completely destroyed in early 2014 by a close encounter with Sgr A* at a distance of 3,000 times the radius of the black hole’s event horizon.
“But G2 survived and continued happily on its orbit; a simple gas cloud would not have done that. G2 was basically unaffected by the black hole,” said Prof Andrea Ghez of the University of California Los Angeles, who is a co-author of the paper published in the Astrophysical Journal Letters (arXiv.org preprint).
Prof Ghez, Dr Witzel and their colleagues believe that G2 is a pair of binary stars that had been orbiting Sgr A* in tandem and merged together into an extremely large star, cloaked in gas and dust.
“G2 appears to be just one of an emerging class of stars near the black hole that are created because the black hole’s powerful gravity drives binary stars to merge into one,” Prof Ghez said.
She added: “when two stars near the black hole merge into one, the star expands for more than 1 million years before it settles back down.”
“This may be happening more than we thought. The stars at the center of the galaxy are massive and mostly binaries. It’s possible that many of the stars we’ve been watching and not understanding may be the end product of mergers that are calm now.”
The team also determined that G2 appears to be in that inflated stage now.
The object has fascinated many astronomers in recent years, particularly during the year leading up to its approach to the black hole.
“It was one of the most watched events in astronomy in my career,” Prof Ghez said.
“G2 now is undergoing a ‘spaghetti-fication’ – a common phenomenon near black holes in which large objects become elongated.”
At the same time, the gas at G2’s surface is being heated by stars around it, creating an enormous cloud of gas and dust that has shrouded most of the massive star.
“We are starting to understand the physics of black holes in a way that has never been possible before,” Prof Ghez concluded.
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G. Witzel et al. 2014. Detection of Galactic Center Source G2 at 3.8 μm during Periapse Passage. ApJ 796, L8; doi: 10.1088/2041-8205/796/1/L8
