Not Quite a Supermassive Black Hole—Midsize Compact Dead Star Found In Messier 82 Galaxy
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Sifting through archival data from NASA's Rossi X-ray Timing Explorer (RXTE) satellite, a team of astronomers have discovered the brightest X-ray source in the galaxy Messier 82 is a rare pulsating black hole nearly 12 million light-years away, according to a study published in this week's issue of the journal Nature.
Thought to have been a midsize black hole for over a decade, a rare occurrence for most, the black hole named "M82 X-1" emitted rhythmic pulsations of X-rays that helped astronomers pinpoint its location and measure its size.
"Between two extremes of stellar and supermassive black holes, it's a real desert, with only about half a dozen objects whose inferred masses place them in the middle ground [like M82 X-1]" astrophysicist at NASA's Goddard Space Flight Center, Tod Strohmayer says.
While most black holes formed by dying stars are modestly sized around 25 times the mass of our sun and most supermassive black holes (formed in large galaxies) contain tens of thousands of times more mass, M82 X-1 was measured to have roughly 400 solar masses thanks to the fluctuating X-rays emitted by the black hole.
As cosmic gases draw nearer to black holes, the gases are heated to another energy level and they emit X-rays, in a variation of brightness depending on the changes it undergoes. Fluctuating wavelengths, which astronomers call "quasi-periodic oscillations" or QPOs for short, are common occurrences for all black holes, but are quite difficult to decipher.
"When we study fluctuations in X-rays from many stellar-mass black holes, we see both slow and fast QPOs" UMCP Graduate Student Dheeraj Pasham says. "But the fast ones often come in pairs, with a specific 3:2 rhythmic relationship."
Looking to M82 X-1 and analyzing six years of RXTE's data, the team of astronomers was able to ultimate determine the stellar-mass of the black hole on a standardized scale once they discovered that the emissions also followed a 3:2 relationship. X-ray variations in brightness and wavelength were found to repeat about 5.1 and 3.3 times each second, and presence of slow QPOs with fast pairs in 3:2 rhythm sets led the team to their discover.
Although RXTE was decommissioned in 2012, after 7 years in space, the data collected continues to provide valuable insights into environments of black holes and neutron stars, which exist in distant galaxies. Researchers are also looking forward as NASA has announced the development of a new X-ray mission called the "Neutron Star Interior Composition Explorer" (NICER), which is scheduled to launch from the International Space Station at the tail-end of 2016.
