May 11, 2000
Vol. 19 No. 16

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    Sloan Survey astronomers identify most distant object

    By Steve Koppes
    News Office

    Astronomers working on the Sloan Digital Sky Survey project have discovered the most distant object ever identified, a quasar some 27 billion light years from Earth.

    The quasar turned up in data taken in March by Sloan Survey astronomers, said survey spokesman Michael Turner, the Bruce V. and Diana M. Rauner Professor in Astronomy & Astrophysics.

    Quasars are compact, luminous objects powered by super-massive black holes. They are not a distinct class of objects but a phase that young galaxies go through when the black holes at their centers pull in surrounding matter at a high rate. The newly discovered quasar has a redshift of 5.8, which means that astronomers are seeing light that left its source when the universe was in its infancy, less than a billion years old. Redshift refers to the amount by which light from a distant object is shifted toward the red end of the spectrum by the expansion of the universe. Astronomers use redshift as a measure of the distance of celestial objects: the higher the redshift, the greater the distance and the younger the universe when the light was emitted.

    The new quasar breaks the distance record previously held by a galaxy with redshift 5.7, which was discovered last year by astronomers at the University of Hawaii and the Institute of Astronomy in Cambridge, England. Twice before, Sloan Survey scientists found quasars that were more distant than any others known previously. To date, the survey has discovered 1,000 quasars, including eight of the 10 most distant, known quasars and two-thirds of the quasars with redshifts greater than 4.5.

    When Princeton University graduate student Xiaohui Fan spotted the new quasar in the data taken by the Sloan Survey’s 2.5-meter telescope at Apache Point, N.M., its distinctively red color showed it to be a likely candidate for a very distant quasar. Fan, along with Marc Davis, professor at the University of California, Berkeley; Robert Becker, professor at the University of California, Davis; and Richard White, astronomer at the Space Telescope Science Institute, used the 10-meter Keck telescope in Hawaii to measure the quasar’s spectrum and confirm that it is indeed the most distant object ever found. A number of objects are candidates for a redshift higher than 6, but their redshifts have not been confirmed by spectra.

    The real significance of the Sloan quasars is not their record-breaking distance but the size and quality of the sample, said Sloan Survey project scientist James Gunn of Princeton University. The data will allow scientists to use quasars to chart the birth and formation of galaxies, explore structure on the largest scales and better understand black holes. Past quasar surveys have included a smaller, less uniform selection of objects.

    Richard Kron, Professor in Astronomy & Astrophysics, said the Sloan project’s quasar advantage comes from the size of the survey and its unique ability to look at objects across five precisely measured color bands.

    Distant quasars, which are extremely rare in the universe, take on the appearance of very red stars, Kron explained. Because the Sloan Survey digitizes images of 20,000 objects in every square degree of sky, the accurate color information and the survey’s recipe for quasar selection are critical to distinguish distant quasars from everything else.

    The Sloan Digital Sky Survey will ultimately survey one-quarter of the sky and 200 million celestial objects. Of these, a million or so will be quasars.

    “You haven’t seen anything yet,” said Donald York, the Horace Horton Professor in Astronomy & Astrophysics and the Sloan Survey’s first director. “By the time the Sloan Survey is done, it will rewrite the book on quasars and the early evolution of galaxies, as well as many other topics in astronomy.”

    During the week that followed the discovery’s announcement, the Sloan Survey’s Web site at Fermi National Accelerator Laboratory, http://www.sdss.org, received more than a million hits.

    “Our previous average was 3,000 to 4,000 per day,” said Sloan Survey Web master Craig Wiegert, a Chicago graduate student in physics.

    The Sloan Survey is a joint project of the University, Fermilab, the Institute for Advanced Study, the Japan Participation Group, Johns Hopkins University, the Max-Planck-Institute for Astronomy, Princeton University, the U.S. Naval Observatory and the University of Washington. The Astrophysical Research Consortium operates Apache Point Observatory. Funding for the project has been provided by the Alfred P. Sloan Foundation, the Sloan Digital Sky Survey member institutions, the National Aeronautics and Space Administration, the National Science Foundation, the U.S. Department of Energy and Monbusho.