From Chandra website NGC 4178: Revealing a Mini-Supermassive Black Hole
Nathan Secrest, ( SPACS graduate student) , and faculty Shobita Satyapal, Mario Gliozzi, el all discovers black hole
“The black hole is located in the middle of the spiral galaxy NGC 4178, shown in this image from the Sloan Digital Sky Survey. The inset shows an X-ray source at the position of the black hole, in the center of a Chandra image (roll your mouse over the image above). An analysis of the Chandra data, along with infrared data from NASA’s Spitzer Space Telescope and radio data from the NSF’s Very Large Array suggests that the black hole is near the extreme low-mass end of the supermassive black hole range.”
And more from Mason News Nov 1, 2012
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.
Secrest, a PhD student in physics, made this observation as part of his research group led by Shobita Satyapal, associate professor in Mason’s 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.
Write to Tara Laskowski at email@example.com
Also featured in a New Scientist article about Loner Galaxies.
Astrophile is our weekly column on curious cosmic objects, from the solar system to the far reaches of the multiverse
Object: NGC 4178, a pristine lone galaxy
Mass: 10,000 to 1 million solar masses
NGC 4178 enjoyed the single life. Even though the flat, disc-shaped galaxy was getting on a bit, it had a svelte spiral figure to be proud of. Its central black hole was perfect: not too small, not too large. It had never been involved in a major merger with another galaxy, and wanted to keep it that way. None of the unsightly bulges and warps associated with too much socialising for NGC 4178.
….They are more representative of the initial stuff, from when structure started to form in the universe,” says Nathan Secrest, a graduate student at George Mason University in Fairfax, Virginia. Galaxies like NGC 4178 are about “as pristine as you can get”.
…”We’ve been looking around and trying to find these galaxies with no bulges,” Secrest says. “We’ve been slowly determining that many of them do in fact have black holes.”
…The fact that several such pristine galaxies turn out to have a small, still-expanding black hole at their core suggests that black holes can grow to intermediate size without mergers, but then need to pool their resources to get much bigger. This supports the idea that supermassive black holes form as a result of galactic unions, Secrest says. In other words, the black hole at NGC 4178’s core could be an example of a seed from which larger black holes could grow.
…But NGC 4178 will not be a singleton forever. The galaxy sits at the edge of the Virgo cluster of galaxies, and will enter the main part of the cluster in the next 100 million years or so.
“It will definitely at some point go through a merger,” Secrest says. When it does it will probably develop a central bulge and a supermassive black hole, just like its more social neighbours. “In some ways, its pristineness will be lost,” Secrest says – but at least it will have made some friends.