06Aug2017

How Large Can Black Holes Be?

Credit: X-ray: NASA/CXC/Stanford/Hlavacek-Larrondo, J. et al; Optical: NASA/STScI; Radio: NSF/NRAO/VLA

Thanks to a new study done with data from NASA’s Chandra X-Ray Observatory, scientists will be re-thinking just how big a black hole can be. It’s been a complete mystery for decades. Right now a “supermassive” black hole, usually located in the center of a galaxy – might not be the end-all of size.  By studying the brightest galaxies located in a sample of eighteen galaxy clusters, astronomers have been zeroing in on the largest black holes seen to date.

This new anaylsis leads them to speculate that at least ten of the targeted galaxies contain “ultra-massive” black holes – monsters that weigh in between 10 to 40 billion times solar mass. Huge? You bet. And these “ultra-massive” specimens only have a few confirmed examples.

larger animation

Black hole simulation (Photo credit: Wikipedia)

“Our results show that there may be many more ultramassive black holes in the universe than previously thought,” said study leader Julie Hlavacek-Larrondo of Stanford University and formerly of Cambridge University in the UK.

Just how were these ultra-massive black holes confirmed? Researched estimated the masses of the black holes in the samples by using an established rationship of black hole mass to x-ray and radio wave output… a process known as the fundamental plane of black hole activity.

This process fits known data on black holes which range between 10 solar masses to a billion solar masses. Hlavacek-Larrondo and her colleagues discovered these ulta black holes were about 10 times larger than standard and one of these relationships involved a correaltion between black hole mass and infrared luminosity of the galactic core.

“These results may mean we don’t really understand how the very biggest black holes coexist with their host galaxies,” said co-author Andrew Fabian of Cambridge University. “It looks like the behavior of these huge black holes has to differ from that of their less massive cousins in an important way.”

So, do ultra-massive black holes simply roam around? No. All of these potential monsters are located in central galaxies housed in huge galactic clusters – areas where huge amounts of hot gases exist. Thanks to outbursts from these central black holes, the gases are constantly heated. This process doesn’t allow the gas to cool and form stars. To keep the outburts going, the black holes themselves consume a considerable amout of mass – the largest of which ingests the most mass and produces the largest outbursts.

“Because the largest black holes can swallow the most mass and power the biggest outbursts, ultramassive black holes had already been predicted to exist, to explain some of the most powerful outbursts seen. The extreme environment experienced by these galaxies may explain why the standard relations for estimating black hole masses based on the properties of the host galaxy do not apply.”

However, the work isn’t finished yet. To confirm ultra-massive black holes, a detailed mass study must estimate the black holes in the sample and model the motion of the stars and gas in its neighborhood. Right now a study of this type has been conducted on the center of Messier Object 87, the central galaxy in the Virgo Cluster. It was chosen because the mass of the black hole, estimated from stellar motion, appears to be higher than the estimate taken from infrared data which is a close match for the Chandra study.

“Our next step is to measure the mass of these monster black holes in a similar way to M87, and confirm they are ultramassive. I wouldn’t be surprised if we end up finding the biggest black holes in the Universe,” said Hlavacek-Larrondo. “If our results are confirmed, they will have important ramifications for understanding the formation and evolution of black holes across cosmic time.”

Original Story Source: Chandra X-Ray Observatory News Release. Reported by Tammy Plotner for Dave Reneke’s World of Space and Astronomy News.

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