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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