Tour of Sagittarius A*
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At the heart of the Milky Way galaxy, there is a supermassive black hole that has the mass equivalent of some four million Suns. Astronomers think that nearly every galaxy has such a black hole at its center. For reasons that scientists don't fully understand, the Milky Way's black hole - known as Sagittarius A* -- is unusually quiet compared to similarly sized black holes in other galaxies. Recently, however, there was a change in the behavior of Sagittarius A*. This was discovered thanks to a long-term monitoring campaign of the black hole by three orbiting X-ray telescopes: NASA's Chandra X-ray Observatory, ESA's XMM-Newton, and NASA's Swift Gamma Ray Burst Explorer. Since 1999, these telescopes in space have periodically observed Sagittarius A*.

While things have been relatively quiet from the black hole over most of the past decade and a half, astronomers saw an increase in flares in the middle of 2014. This was several months after scientists predicted a dusty object, called G2, would be making a close approach to the black hole. It's possible that G2 got so close that the strong gravitational pull of black hole grabbed some of its dust, sending it down toward the black hole and heating it up to temperatures where it glowed in X-rays. While the timing is intriguing, it's not an open and shut case. For example, the uptick of X-rays could be the result of a change in the strength of winds from nearby massive stars that are feeding the black hole. Astronomers will continue to observe Sagittarius A* with Chandra and other telescopes and hope that additional data will shed light on the questions surrounding our Galaxy's supermassive black hole.
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(Credit: NASA/CXC/A. Hobart)