Measurement Confirms Presence Of Intermediate Mass Black Hole In Nearby Galaxy
Astronomers from the University of Maryland and NASA's Goddard Space Flight Center in Greenbelt, Maryland have accurately measured and confirmed the existence of a black hole roughly 400 times the mass of our sun.
Black holes that range in size from about 10 to 100 times the mass of our sun are the remnants of dying stars, while much larger supermassive black holes are more than one million times our sun's mass and typically inhabit the centers of most galaxies. However, there is a third type of black hole - intermediate mass black holes.
Intermediate mass black holes are between 100 and 10,000 solar masses in size, and tend to be scattered throughout the universe. In fact, these phenomena are so difficult to locate and measure that some scientists dispute their existence. It is unknown if they behave like other black holes, and little information is available about how they form.
Now, however, University of Maryland astronomy graduate student Dheeraj Pasham, fellow student Richard F. Mushotzky and Tod E. Strohmayer of Goddard's Astrophysics Science Division and Joint Space-Science Institute have measured an intermediate black hole located 12 million light years from Earth in galaxy M82.
"Objects in this range are the least expected of all black holes. Astronomers have been asking, do these objects exist or do they not exist? What are their properties? Until now we have not had the data to answer these questions," Mushotzky explained on Sunday.
While it is not the first intermediate mass black hole ever discovered, it is the first to be precisely measured, "establishing it as a compelling example of this class of black holes," he added. The findings, which are based on observations made with the Rossi X-ray Timing Explorer (RXTE), are detailed in Sunday's edition of the journal Nature.
[ Watch: RXTE Satellite Catches The Beat Of A Midsize Black Hole ]
Black holes are regions of space that contain a mass so dense that not even light can escape its gravity, the researchers explained. While they are technically invisible, astronomers can detect them by tracking their gravitational pull on other objects. The matter being pulled into a black hole, which they compare to the storm debris that circles around the center of a tornado, rubs together and produces light and friction.
Over the past several decades, astronomers have observed several hundred objects that they believe might have been intermediate mass black holes. However, since they could not measure the mass of these objects, they could not be certain. Mushotzky explained that these objects have proven resistant to standard measurement techniques for reasons which are not entirely understood by the scientific community.
Pasham focused on one specific object in M82, which is the closest starburst galaxy to Earth and is located in the constellation Ursa Major. In 1999, NASA's Chandra X-ray Observatory detected X-rays from a bright object located there. The object, which was named M82 X-1, had long been suspected of being an intermediate mass black hole. However, estimates of its mass alone were not enough to confirm those suspicions.
From 2004 through 2010, the RXTE made approximately 800 observations of M82 X-1, recording individual x-ray particles emitted by the object in the process. The wavelength and intensity of the x-rays in each sequence were mapped by Pasham, who then put each of the sequences together and analyzed the result.
"Among the material circling the suspected black hole, he spotted two repeating flares of light. The flares showed a rhythmic pattern of light pulses, one occurring 5.1 times per second and the other 3.3 times per second - or a ratio of 3:2," the university explained. "The two light oscillations were like two dust motes stuck in the grooves of a vinyl record spinning on a turntable," noting that they "would produce a specific syncopated rhythm" as if they were musical beats.
Using the oscillations, Pasham estimated that M82 X-1 is 428 times the mass of the sun, plus or minus 105 solar masses. Currently, he cannot explain how this class of black holes formed, stating that he and his colleagues "needed to confirm their existence observationally first. Now the theorists can get to work."
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