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Astronomers observe most distant object in Universe
Posted: April 14, 2000

The arrow in this image points to the most distant quasar ever observed, with a record-shattering redshift of 5.8. SDSS astronomers identified this faint speck of light as a possible quasar based on its distinctive red color. A spectrum of this object, obtained with the 10-meter Keck telescope in Hawaii, showed that this was indeed a quasar with a most impressive redshift. Photo: SDSS Collaboration
The distinctive palette of colors in its light told scientists that the bright red object they were studying wasn't just another star. Indeed, last week, when astronomers analyzed the spectrum from the quasar they had found, they realized they were seeing light that had left its source at time when the universe was a baby, a mere infant of less than a billion years old.

They were looking at the most distant object human beings had ever identified.

This farthest of the quasars -- compact yet luminous objects thought to be powered by black holes as massive as a billion suns -- turned up in data taken in March, 2000, by astronomers of the Sloan Digital Sky Survey, said the Survey's spokesman, Dr. Michael S. Turner of the University of Chicago and the Department of Energy's Fermilab.

"The newly discovered quasar has a red shift of 5.8," Turner said. "Redshift is 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, discovered last year by Esther Hu and colleagues at the University of Hawaii and the Institute of Astronomy in Cambridge, UK. Moreover, -- and ultimately perhaps much more significant -- this isn't the first far-off quasar the Sky Survey has found.

"Finding record-breaking quasars has become something of a habit for the Sky Survey," said SDSS astronomer Professor Michael Strauss, of Princeton University. "Twice before, SDSS scientists have found quasars more distant than any found before. To date, SDSS has discovered some thousand quasars, including eight of the ten most distant known quasars and two-thirds of the quasars with redshifts greater than 4.5 -- a quasar harvest that is the more remarkable because it comes from data gleaned from the early engineering phase of the Sky Survey."

Just a few weeks ago, two SDSS astronomers, Johns Hopkins University research scientist Wei Zheng and JHU Associate Research Professor Zlatan Tsvetanov, discovered what is now the second most distant SDSS quasar, with a redshift of 5.3. Zheng and Tsvetanov were among the first to congratulate the team that broke their record.

According to SDSS astronomer Professor Richard Kron of the University of Chicago and Fermilab, the SDSS 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. "Since the Sky Survey digitizes images of 20,000 objects in every square degree of sky, the accurate color information and the Sky Survey's recipe for quasar selection are critical to distinguish very distant quasars from everything else."

When SDSS astronomer and Princeton graduate student Xiaohui Fan spotted the new quasar in the Sky Survey data he was studying based on observations made in March 2000, its distinctively red color showed it to be a likely candidate for a very distant quasar. Fan, University of California at Berkeley Professor Marc Davis, UC Davis Professor Robert Becker, and astronomer Richard L. White of 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. While there are number of intriguing candidate objects for redshifts higher than 6, their spectra have not yet been taken.

"Without a confirming spectrum," said Berkeley's Davis, "the discovery of a high-redshift object doesn't really count."

While setting distance records is exhilarating, Sky Survey astronomers said, the meaning of such discoveries goes far beyond the distance scorecard. The great power of the SDSS is to find so many of these candidates, with its wide field-of-view, and to do so with such a high probability of success.

SDSS Project Director John Peoples poses at sunset in front of the 2.5-meter Survey telescope, located at Apache Point Observatory in New Mexico. Photo: Dan Long, Apache Point Observatory
"The real significance of the Sloan quasars," said SDSS Project Scientist James Gunn of Princeton University, "is not their record-breaking distances but the size and quality of the sample. The scale and the homogeneity of the data will allow SDSS and other 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 and less uniform selection of objects. When the Sky Survey is complete, it will have combed one quarter of the sky, using uniform selection criteria."

Sky Survey astronomer Donald Schneider, a Pennsylvania State University professor, noted that our current understanding of very high redshift quasars is based on samples of a dozen or so objects assembled over many years of observation.

"In the past eighteen months," Schneider said, "SDSS has more than doubled the number of known quasars with redshifts above 4.5."

Already, said Princeton's Fan, he and others have used the early Sloan sample to trace the time history of quasar populations. Consistent with earlier studies, the SDSS data show that the number of quasars rose dramatically from a billion years after the big bang to a peak around 2.5 billion years later, falling off sharply at lower redshift and hence later times.

Indeed, said SDSS astronomer and Princeton researcher Robert Lupton, the new quasar is sure to attract more than its share of attention from astronomy groups at the biggest telescopes in the world.

"Because it is so exceptionally luminous, it provides a wonderful opportunity to study the universe when the galaxies that we see today were young," Lupton said, "or perhaps before they had even been born."

University of Chicago Professor Donald York, one of the Sky Survey initiators and a well-known quasar maven himself, went a step further.

"You haven't seen anything yet," York said. "By the time the Sloan Survey is done, it will rewrite the book on quasars and the early evolution of galaxies, as well as on many other topics in astronomy."

The Sloan project will ultimately survey 10,000 square degrees, or one quarter of the sky, and 200 million celestial objects. Of these, a million or so will be quasars, and the Sky Survey's 2.5-meter special-purpose telescope will determine distances for some 100,000 of the brightest. Telescopes around the world (including the 3.5-meter ARC telescope, near the Sky Survey telescope at Apache Point, N.M. site, and the 9.2 meter Hobby-Eberly telescope at McDonald Observatory in Texas) will follow up on these new quasars.

The Sloan Digital Sky Survey (SDSS) is a joint project of The University of Chicago, Fermilab, the Institute for Advanced Study, the Japan Participation Group, The Johns Hopkins University, the Max-Planck-Institute for Astronomy, Princeton University, the United States Naval Observatory, and the University of Washington. Apache Point Observatory, site of the SDSS, is operated by the Astrophysical Research Consortium. Funding for the project has been provided by the Alfred P. Sloan Foundation, the SDSS member institutions, the National Aeronautics and Space Administration, the National Science Foundation, the U.S. Department of Energy, and Monbusho. The Keck 10-meter telescope, the world's largest, is jointly operated by the University of California, Caltech, the University of Hawaii and NASA.

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