Hints of Second Largest Black Hole in Our Galaxy Detected

January 21, 2016 | Joanne Kennell

Photo credit: A Milk drop falling into a bowl of water. Looks like a Black Hole.

Did I mention it is also invisible?

There may be another giant black hole hiding within our galaxy, and the reason it had not been found after all this time is because it is invisible.  However, some interesting signs that point to its existence have recently been discovered.

A team of astronomers led by Tomoharu Oka, a professor at Keio University in Japan, found a gas cloud, creatively named CO-0.40-0.22, only 200 light years away from the center of the Milky Way.  What makes this gas cloud so intriguing is that it has a surprisingly wide velocity dispersion, meaning that the cloud contains gas with a very wide range of speeds.

To investigate the clouds structure, the team used the Nobeyama 45-m Telescope to obtain 21 emission lines from 18 molecules.  Their results showed that the cloud has an elliptical shape and consists of a compact but low density component with a very wide velocity dispersion of 100 km/s, and a high density component spanning 10 light years with a narrow velocity dispersion.

So the question is: Why is the velocity dispersion so wide?

There are no holes inside the cloud, nor are there any signs of a compact object that would indicate that this dispersion is caused by some sort of local energy input, such as a supernova explosion.

SEE ALSO: Light Holograms Preserve Black Hole Information, According to Stephen Hawking

To figure out what could be causing the dispersion, the team performed a simulation of gas clouds moving around by a strong gravity source.  In fact, when the team used a gravity source 100,000 times the mass of the sun inside an area with a radius of 0.3 light years, the results closely matched the observed data .

“Considering the fact that no compact objects are seen in X-ray or infrared observations,” said Oka, the lead author of the paper that appeared in Astrophysical Journal Letters, “as far as we know, the best candidate for the compact massive object is a black hole.”

Now if it is a black hole, it would be the first time an intermediate mass black hole has ever been detected.  Astronomers have already observed two other sizes of black holes: stellar-mass black holes, formed after the gigantic explosions of very massive stars; and supermassive black holes (SMBH), often found at the center of galaxies, such as Sagittarius A* found at the center of our Milky Way.

Although many SMBHs have been detected, no one is really sure how they form.  One theory was that they are formed from the merging of many intermediate mass black holes.  However, this idea was problematic because no one had ever detected one... until now.  So if CO-0.40-0.22 really is an intermediate mass black hole, we may be one step closer to understanding the evolution of SMBHs.

Not only that, the results may lead to a new method of searching for black holes — using radio telescopes.  Recent observations have revealed that this gas cloud is not the only one out there.  There are actually a number of wide-velocity-dispersion clouds, and maybe some of them contain black holes.

“Investigations of gas motion with radio telescopes may provide a complementary way to search for dark black holes” said Oka. “The on-going wide area survey observations of the Milky Way with the Nobeyama 45-m Telescope and high-resolution observations of nearby galaxies using the Atacama Large Millimeter/submillimeter Array (ALMA) have the potential to increase the number of black hole candidates dramatically.”

Who knows how many other invisible black holes may be out there, but I have a feeling CO-0.40-0.22 is not the only one!

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