Quasar quandary upsets cosmic status quo.
These provocative findings emerge from the detection of extremely distant quasars -- massive, highly luminous powerhouses thought to lie at the center of some galaxies. Finding just a couple of these objects, as reported last month (SN: 5/4/91, p.276), might not carry enough statistical significance to challenge theoretical models of how and when the universe developed its complex structure. But last week, astronomers announced they had detected another 27 distant quasars -- a discovery that may provide the most compelling reason yet for modifying our notions about cosmic evolution after the Big Bang.
An analysis of images from the U.K. Schmidt Telescope at Epping, Australia, reveals that the most distant luminous quasars ever observed have the same density as those closer to Earth, report Richard McMahon and Michael Irwin of the University of Cambridge in England. Since viewing distant objects is essentially the same as peering back through time, this finding suggests that the universe contained about as much lumpiness when it was just 7 percent of its current age -- the first billion or so years of its existence -- as at later times.
"The present generation of theories can't explain this," McMahon says.
As recently as a decade ago, astronomers had found no extremely distant quasars -- those with spectra shifted strongly to the red -- and most didn't believe the objects existed, McMahon notes. But by using a computer scanning technique and special color criteria to analyze millions of images on photographic plates, McMahon and his collaborators found 20 quasars that rank among the most distant objects known.
All of the 20 quasars have a redshift between 4 and 5, which means they lie an estimated 10 to 12 billion light-years from Earth. McMahon and Irwin described these findings -- which increase the number of known objects in this high-redshift range to about 33 -- at a quasar workshop last week in Victoria, British Columbia.
Another seven quasar discoveries emerged from a project in which McMahon compared radio sources found by the Very Large Array in Socorro, N.M., with corresponding visible-light images from a sky survey conducted at Mount Palomar in California. He identified 11 radio-loud quasars with redshifts between 3 and 4. The seven new ones, he says, include the most distant radio quasar ever detected -- lying more than 10 billion light-years from Earth.
McMahon says the relatively large number of high-redshift radio quasars he detected further supports the notion that the density of bright quasars doesn't diminish at far distances. At the same workshop, Maarten Schmidt of Caltech in Pasadena reported data suggesting that the density of less luminous quasars may decline beyond distances corresponding to a redshift of 3.
Theorists have yet to come to terms with "these improbable monsters," observes cosmologist Edward L. Turner of Princeton (N.J.) University. And this mother lode of distant quasars may represent just the first of many such challenges. Looming ahead, notes McMahon, are radio surveys that will search for quasars so distant and so highly redshifted that they would not appear on photographic plates.
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|Title Annotation:||discovery of distant quasars may force a revision of cosmic evolution theory|
|Date:||Jun 15, 1991|
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