Astronomers have discovered the smallest supermassive black hole lurking in the center of a dwarf galaxy around 340 million light-years away. Small it may be, but it could help to unlock some pretty hefty black hole mysteries.
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The black hole was discovered in the dwarf galaxy RGG 118. It's the smallest supermassive black hole discovered to date, but it still “weighs in” at a whopping 50,000 times the mass of our sun. However, it is less than half the mass of the next-smallest supermassive black hole discovered to date and 100 times less massive than the supermassive black hole that lives in the center of our galaxy.
As we’re comparing, RGG 118′s black hole is 200,000 less massive than the biggest supermassive black hole known to exist.
Size comparisons to one side, this latest black hole discovery is extremely important to astronomers trying to understand the perplexing evolutionary processes that dominate supermassive black holes, which are known to reside in the majority of galaxies, and how they relate to their host galaxy’s evolution.
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“It might sound contradictory, but finding such a small, large black hole is very important,” said Vivienne Baldassare of the University of Michigan in Ann Arbor, in a NASA news release. “We can use observations of the lightest supermassive black holes to better understand how black holes of different sizes grow.”
RGG 118 was originally discovered by the Sloan Digital Sky Survey. Baldassare’s team used NASA’s Chandra X-ray Observatory and the 6.5-meter Clay Telescope in Chile to characterize the surprisingly small supermassive black hole. They were able to study the motion of cool gas in the center of RGG 118 in optical light using the Clay Telescope. They also zoomed in on the X-ray emissions from the hot, swirling gas in close proximity to the black hole using Chandra. Both of these measurements proved that RGG 118′s black hole acts in a similar way to other supermassive black holes in the centers of other galaxies.
The velocities of stars surrounding the black hole in the core of the galaxy also supported this finding.
A Sloan Digital Sky Survey image of RGG 118, a galaxy containing the smallest supermassive black hole ever detected. The inset is a Chandra image showing hot gas around the black hole.
NASA/CXC/UNIV OF MICHIGAN/V.F.BALDASSARE, ET AL; OPTICAL: SDSS
“We found this little supermassive black hole behaves very much like its bigger, and in some cases much bigger, cousins,” added co-author Amy Reines of the University of Michigan. “This tells us black holes grow in a similar way no matter what their size.”
One of the biggest mysteries in modern astrophysics is the existence of seriously massive, billion-solar mass supermassive black holes that must have existed in the universe less than a billion years after the Big Bang. Astronomers hope that through the discovery of this smaller example that black hole evolution models may be refined.
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Currently, it is theorized that supermassive black holes are either seeded by the rapid collapse of vast gas clouds with masses of up to 100,000 times that of our sun or they are formed by the collapse of massive stars. Now we have the opportunity to see which model is more likely in the case of RGG 118.
“We have two main ideas for how these supermassive black holes are born,” said Elena Gallo, also of the University of Michigan. “This black hole in RGG 118 is serving as a proxy for those in the very early universe and ultimately may help us decide which of the two is right.”
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