A Dark Discovery: Mason PhD Student Identifies a Mini-Supermassive Black Hole
By Tara Laskowski
One of the lowest mass supermassive black holes ever observed in the middle of a galaxy has been identified, thanks to Mason student Nathan Secrest and other researchers using NASA’s Chandra X-ray Observatory. (Video)
Secrest, a PhD student in physics, made this observation as part of his research group led by Mason astrophysicist Shobita Satyapal, a professor in the School of Physics, Astronomy, and Computational Sciences (SPACS). Secrest is funded by the Chandra Guest Investigator Program under a NASA grant.
The host galaxy of the black hole, a spiral galaxy called NGC 4178 located about 55 million light years from Earth, is of a type not expected to harbor supermassive black holes, suggesting that this black hole may have a different origin.
While most black holes have masses that are typically millions to billions of times the mass of the sun, this black hole is estimated to have a mass of about only 200,000 times that of the sun. The results and image of this observation were published in the July 1, 2012, issue of The Astrophysical Journal.
The team used X-rays to find the black hole, which would have been hidden from detection using the more common optical surveys.
“We know a lot about stellar-mass black holes [less than 100 solar masses] and we know a lot about supermassive black holes [greater than 1 million solar masses], but we know very little about intermediate-mass black holes, and we think that they may lurk at the center of this type of galaxy,” says Secrest. “Building up statistics on these black holes will help us narrow down the many theories that exist for the formation of nuclear black holes in the early universe.”
Despite its low mass, NGC 4178 is rapidly pulling in material from its surroundings, says Secrest. Data generated also suggest that light generated by this material is heavily absorbed by gas and dust surrounding the black hole.
“NGC 4178 does not contain a bright central concentration, or bulge, of stars in its center, which is unusual for a galaxy that hosts a supermassive black hole,” says Satyapal, the principal investigator on the project and Secrest’s thesis advisor at Mason.
Besides NGC 4178, only four other galaxies without bulges are currently thought to contain supermassive black holes. Of these four black holes, two have masses that may be close to that of the black hole in NGC 4178.
Previously, astronomers have found that observations of a large number of galaxies are consistent with a close correlation between the mass of a supermassive black hole and the mass of the bulge of its host galaxy. Theoretical models developed to explain these results invoke mergers of galaxies and predict that galaxies without bulges are unlikely to host supermassive black holes. The results found for NGC 4178 and the four other galaxies mentioned run counter to these predictions and may suggest that more than one mechanism is at work in forming supermassive black holes.
Other co-authors on the project include Mario Gliozzi, research assistant professor in SPACS; Teddy Cheung from the National Academy of Sciences in Washington, D.C.; Anil Seth from the University of Utah; and Torsten Boeker from the European Space Agency/European Space Research and Technology Centre in the Netherlands.
This article originally appeared on the university’s News site.
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