Giant cluster confounds cosmology.

Astronomers have discovered a cluster of 10 quasars that may represent the largest structure ever found in the universe -- as well as one of the most distant. Covering a swath at least 650 million light-years long and 100 million light-years wide in the northern celestial hemisphere, this quasar cluster is only the third identified so far. Its discovery adds to a growing body of evidence challenging several theories commonly invoked to explain the evolution of the universe.

Roger G. Clowes of the Royal Observatory in Edinburgh, Scotland, and Luis E. Campusano of the University of Chile in Santiago used two telescopes to detect the quasars. About five years ago, Clowes and Campusano began using an automated scanning machine to examine and digitize tens of thousands of images from a photographic plate taken by the U.K. Schmidt Telescope in Epping, Australia. Keying in on such features as the brightness and color of the imaged objects, special software then selected about 200 likely candidates for quasars from among the myriad galaxies and stars depicted on the plate.

Two years ago, guided by their list of quasar candidates, the researchers made high-resolution observations of the same sky region using the 4-meter telescope at the Cerro Tololo Inter-American Observatory in Chile. The study confirmed about 20 of the 200 objects as quasars, based on their redshifts and spectra. Moreover, 10 of these turned out to be astronomical neighbors. Their redshifts all fell within the range of about 1.1 to 1.3, indicating that they sit relatively close together at a distance of perhaps 8 billion light-years from Earth, Clowes says. Three quasars identified in a nearby sky region in the 1980s may belong to the same group, he adds.

Clowes notes that the cluster appears to exceed the dimensions of the two other known quasar groups, discovered in 1982 and 1989. But because the newly identified cluster -- as well as the one found in 1989 -- may stretch beyond the boundaries of the photographic plates, their relative sizes remain unclear, he says.

Nonetheless, the average redshift of quasars in the newly found cluster indicates that Earth-based observers are seeing this structure as it existed when the universe was only one-third its current age. The discovery that a quasar group existed in such an early era confounds the standard assumption that the universe could not have grown so lumpy so soon after the smooth, uniform beginning of the Big Bang. Clowes and Campusano plan to examine photographic plates from other sky regions to find out whether other such clusters may have existed in the early universe.