First Triple Quasar Found, May Shed Light on Early Universe
Richard A. Lovett in Seattle, Washington
for National Geographic News
|January 9, 2007|
The first observed trio of enormous, hyperactive black holes known as quasars has been spied in the constellation Virgo, an international team of astronomers announced yesterday.
Quasars are enormously powerful astronomical objects that emit a galaxy's worth of energy from a region the size of our solar system.
(Related image: a quasar as seen by the Hubble Space Telescope.)
Scientists believe quasars are powered by gas and dust falling into enormous black holes at the heart of some galaxies.
About a hundred thousand quasars are known, of which only about a hundred are believed to be binaries—an orbiting pair of supermassive black holes that come together when two galaxies collide and merge.
"Binaries are rare. This is the first triple," George Djorgovski, an astronomy professor at the California Institute of Technology in Pasadena, said yesterday at a meeting of the American Astronomical Society in Seattle, Washington.
The three quasars are 10.5 billion light-years away from Earth, but are only a hundred thousand light-years apart from each other.
Because light from the quasars has been in transit for billions of years, looking at them is also peering backward into the universe's distant past, astronomers note.
Scientists also expect the discovery to reveal the new and potentially violent ways that three quasars in close quarters might interact.
Most galaxies, including the Milky Way, are thought to have supermassive black holes at their centers, but not all such black holes are quasars.
(Read "Supermassive Black Hole at Center of Milky Way, Study Hints" [November 2, 2005].)
When galaxies collide—something that happens often in their multibillion-year histories—gravitational disturbances can dump large amounts of gas into their central black holes, creating quasars.
"Galaxies are part of an extremely dynamic universe," said Frederic Rasio of Northwestern University in Evanston, Illinois. Rasio was not involved in the discovery but presented related findings at the meeting.
"As they moved around, particularly in early times when things were very crowded because the universe had not yet expanded to its present size, galaxies often ran into each other."
But until now, a triple quasar was considered to be a statistical impossibility.
The discovery came from careful reexamination of a binary quasar that had been found in 1989.
Working with two of the world's largest telescopes—one in Hawaii and another in Chile—the scientists had no trouble seeing the extra speck of light.
The hard part, Djorgovski said, was proving that it wasn't an optical illusion caused by an effect called gravitational lensing.
This distortion occurs when light from a distant object passes close to an intervening object that has enough gravity to bend the light.
The light from one galaxy then splits into mirror images that can appear to be scattered across the sky.
"That is what we first thought [it was]," Djorgovski admitted. But more detailed study indicated that the astronomers were really seeing light from three separate sources.
Djorgovski and colleagues have submitted a paper on their work to the journal Astrophysical Journal Letters.
Result of a Three-Way
Rasio, of Northwestern University, said the triple quasar is most likely the result of a three-way galactic collision.
Gravity will eventually bind the colliding galaxies into one larger unit.
But the three black holes will orbit each other in a complex dance until one or more are ejected into intergalactic space.
Unfortunately, today's astronomers won't be around to see that happen. The galaxies are merely beginning a collision that will take millions of years to complete.
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