University of California, Berkeley, astronomers have discovered the largest black holes to date - two monsters with masses equivalent to 10 billion suns that are threatening to consume anything, even light, within a region five times the size of our solar system.
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| An artist’s concept of stars moving in the central regions of a giant elliptical galaxy that harbors a supermassive black hole |
“In the early universe, there were lots of quasars or active galactic nuclei, and some were expected to be powered by black holes as big as 10 billion solar masses or more,” said Chung-Pei Ma, UC Berkeley professor of astronomy. “These two new supermassive black holes are similar in mass to young quasars, and may be the missing link between quasars and the supermassive black holes we see today.”
Black holes are dense concentrations of matter that produce such strong gravitational fields that even light cannot escape. While exploding stars, called supernovas, can leave behind black holes the mass of a single star like the sun, supermassive black holes have presumably grown from the merger of other black holes or by capturing huge numbers of stars and massive amounts of gas.
“These black holes may shed light on how black holes and their surrounding galaxies have nurtured each other since the early universe,” said UC Berkeley graduate student Nicholas McConnell, first author of a paper on the discovery published in the Dec. 8, 2011 issue of the British journal Nature by McConnell, Ma and their colleagues.
To date, approximately 63 supermassive black holes have been found sitting in the cores of nearby galaxies. The largest for more than three decades was a 6.3 billion solar mass black hole in the center of the nearby galaxy M87.
One of the newly discovered black holes is 9.7 billion solar masses and located in the elliptical galaxy NGC 3842, the brightest galaxy in the Leo cluster of galaxies, 320 million light years away in the direction of the constellation Leo. The second is as large or larger and sits in the elliptical galaxy NGC 4889, the brightest galaxy in the Coma cluster about 336 million light years from Earth in the direction of the constellation Coma Berenices.
According to McConnell, these black holes have an event horizon – the “abandon all hope” edge from which not even light can escape – that is 200 times the orbit of Earth, or five times the orbit of Pluto. 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.
These 10 billion solar mass black holes have remained hidden until now, presumably because they are living in quiet retirement, Ma said. During their active quasar days some 10 billion years ago, they cleared out the neighborhood by swallowing vast quantities of gas and dust. The surviving gas became stars that have since orbited peacefully. According to Ma, these monster black holes, and their equally monster galaxies that likely contain a trillion stars, settled into obscurity at the center of galaxy clusters.
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| NGC 3842 (upper left) is the brightest galaxy in a rich cluster of galaxies. The black hole at its center (shown in middle as artist’s concept) is surrounded by stars distorted by its immense gravitational field. The black hole, which is seven times larger than Pluto’s orbit, would dwarf our solar system (inset) |
Using telescopes at the Gemini and Keck observatories in Hawaii and at McDonald Observatory in Texas, McConnell and Ma obtained detailed spectra of the diffuse starlight at the centers of several massive elliptical galaxies, each the brightest galaxy in its cluster. So far, they’ve analyzed the orbital velocities of stars in two galaxies and calculated the central masses to be in the quasar range. Having such huge masses contained within a volume only a few hundred light years across led the astronomers to conclude that the masses were massive black holes.
“If all that mass were in stars, then we would see their light”, Ma said.
Modeling these massive galaxies required use of state-of-the-art supercomputers at the Texas Advanced Computing Center.
“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.”
Source: UC Berkeley
