December 6, 2011
Monster Galaxies Found To Harbor Record Massive Black Holes
Astronomers from UC Berkeley have discovered the largest black holes to date -- two monstrous abyssal voids with masses equivalent to more than 10 billion suns, threatening to consume everything in its path within a region five times the size of our own solar system.
The massive black holes are at the centers of two galaxies more than 300 million light years away. Such holes could be the gravitational foundations of galaxies and clues to the fates of violent quasars, the powerful explosions in the cores of infant galaxies that dominated the early years of the universe.
The largest of the two black holes, weighs in at nearly 21 billion suns. It is an egg-shaped swirl of stars known as NGC 4889, the brightest galaxy in an expansive cloud of thousands of galaxies roughly 336 million light years away in the Coma constellation.
The other is the equivalent of 9.7 billion suns and lurks in the center of NGC 3842, a galaxy roughly 331 million light years away in the constellation Leo.
“They are monstrous,” Berkeley astrophysicist Chung-Pei Ma told The Telegraph. “We did not expect to find such massive black holes because they are more massive than indicated by their galaxy properties. They're kind of extraordinary.”
Previously, the largest black hole known -- located in the galaxy M87, a member of the Virgo cluster 54 million light years away -- was the mass of 6 billion suns.
The team of scientists used Texas-based supercomputers, ground-based telescopes, and the Hubble Space Telescope to observe stars near the black holes and measure the stellar velocities to uncover the vast regions.
Nicholas McConnell, a Berkeley graduate and lead author of the study, set to be published in the British journal Nature on Wednesday, said it is uncertain how these monstrous black holes originated. To be as massive as they are now, they must have grown considerably since their formation, he said. Black holes are so dense that nothing, not even light, can escape them. Some black holes are formed by the collapse of a super-size star.
Scientists believe that most, if not all, galaxies have black holes at their center. The bigger the galaxy, the bigger the black hole, it would seem. Ma believes the two newly discovered black holes escaped detection for so long because they are living rather peaceful old ages -- much quieter and more boring than their boisterous youth powering quasars billions of years ago.
“For an astronomer, finding these insatiable black holes is like finally encountering people nine feet tall whose great height had only been inferred from fossilized bones. How did they grow so large?” Ma said. “This rare find will help us understand whether these black holes had very tall parents or ate a lot of spinach.”
Oxford University astrophysicist Michele Cappellari, who wrote an accompanying commentary in the journal Nature, agreed that the two newly discovered black holes “probably represent the missing dormant relics of the giant black holes that powered the brightest quasars in the early universe.”
Ma said even larger black holes could be lurking somewhere in the universe. How big can a black hole grow? is the million-dollar question, he said.
The researchers already are peering into the biggest galaxies for answers.
“If there is any bigger black hole,” Ma said, “we should be able to find them in the next year or two. Personally, I think we are probably reaching the high end now. Maybe another factor of two to go at best.”
Ma described it as a kind of nature-versus-nurture argument, explaining that black holes could grow by merging with other black holes as galaxies merge to get bigger – “nature” – or by swallowing gas around them – “nurture.”
“It´s a bit like asking: Are taller children produced by taller parents or by eating a lot of spinach?” Ma wrote in an e-mail to the New York Times. “For black holes we are not sure.”
Martin Rees, a cosmologist at Cambridge University, called the new work “an incremental step,” noting that the study of monster black holes has been a part of his life for a long time. “It´s good to learn about even bigger ones,” he told the New York Times.
Rees, and a colleague at Cambridge, Stephen Hawking, have spent their careers studying the implications for physics of objects that can wrap space-time around themselves like a magician´s cloak and disappear.
To date, approximately 63 supermassive black holes have been found sitting in the cores of nearby galaxies.
According to McConnell, these newly discovered black holes have an event horizon that is 200 times the orbit of Earth. Beyond the event horizon, each black hole has a gravitational influence that would extend over a sphere 4,000 light years across.
“For comparison, these black holes are 2,500 times as massive as the black hole at the center of the Milky Way Galaxy, whose event horizon is one fifth the orbit of Mercury,” McConnell said in a recent press release.
Coauthors of the study are Hubble postdoctoral fellow Shelley A. Wright at UC Berkeley and graduate student Jeremy D. Murphy of the University of Texas; Tod R. Lauer of the National Optical Astronomy Observatory; and Douglas O. Richstone of the University of Michigan.
The research was supported by the National Science Foundation, the National Aeronautics and Space Administration and UC Berkeley´s Miller Institute for Basic Research in Science.
Image 1: Artist's conceptualization of the stellar environment around a black hole of about 10 billion solar masses. The velocity of stars in orbit (and close to) the black hole help to determine its mass. Gemini Observatory/AURA illustration by Lynette Cook.
Image 2: This picture illustrates the immense size of the black holes discovered. The black holes reside at the centers of the two galaxies, each of which is the brightest galaxies in a cluster of galaxies. The background image shows the brightest galaxy in the cluster Abell 1367, which host one of the black holes. The event horizons are several times larger than Pluto's orbit. Our solar system would be dwarfed by the holes. P. Marenfeld/NOAO/AURA/NSF
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