The birth of twin quasars.
Astronomers have resolved a distant, fuzzy patch of light designated PHL 1222 into two separate objects that may represent a pair of quassars less than 100,000 light-years apart. Quasars, thought to be the active cores of certain types of galaxies, are extraordinary bright but relatively small objects that greatly outshine the "host" galaxies enveloping them. The discovery of two so close togeterh indicates the host galaxies may have a strong gravitational influence on each other. That could have been responsible for turning on both quasars, says George Meylan of the Space Telescope Science Institute in Baltimore, who led the team making the discovery.
Astronomers have detected apparent quasar pairs in the past, by those images instead represented light from a single, distant quasar split into two components by the gravitational effects of an intervening galaxy between the quasar and the Earth-based observers. In such gravitationally lensed quasars, both components have identical spectra, confirming that the light comes from the same source. In contrast, the two quasars that make up PHL 1222 have slightly different spectra.
The newly identified quasars also appear to be approaching each other with velocities typical of galaxies in a cluster, and they have a spectral redshift of 1.91, indicating that the light seen was emitted as much as 12 billion years ago. These observations suggest that rich clusters of galaxies may have existed early in the history of the universe, putting a significant constraint on theories attempting to explain the formation of large-scale structure in the early universe.
The discovery of the twin quasars in PHL 1222 also provides evidence that close encounters between galaxies may be responsible for turning on many quasars. Computer simulations show that encounters between galaxies can cause gravitational effects capable of driving huge amounts of gas into the inner regions of the galaxies. Such a mass concentration could develop into a black hole, and matter swirling into the hole would generate prodigious amounts of radiation.
Galactic near-collisions would have been much more common 12 billion years ago, when the universe was smaller and galaxies closer together, the researchers say. That would help explain why the majority of quasars emerged billions of years ago and are now seen at such great distances.
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|Date:||Jan 27, 1990|
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