Breaking the redshift-4 barrier.
For cosmologists, a redshift value of 4 used to seem like the 4-minute mile in footracing. For a long time, in spite of diligent searching, no object with a redshift greater than 4 could be found. Cosmologists wondered whether the horizon of the universe might be somewhere around the distance represented by redshift 4, and so we would never be able to see beyond it. However, it has turned out not to be the horizon, and we do see beyond it.
As with the 4-minute mile, once the barrier was broken, new records were posted swiftly. There are now at least three known quasars with redshifts beyond 4, two of which were reported in the last few weeks, including the most distant object now known, with a redshift of 4.11.
In nature, the most common cause of redshift--a systematic reddening of an object's light--is motion away from the observer. According to the expanding-universe theory, the greater an object's recession velocity, the farther away it is. The redshift of 4.11 translates to a velocity of 93 percent of the speed of light, according to an announcement by the European Southern Observatory (ESO) in Cerro La Silla, Chile.
The first object with a redshift greater than 4 was the quasar 0046-293, with a redshift of 4.01 reported in the Jan. 8, 1987 NATURE by S.J. Warren, and colleagues. from the Institute of Astronomy in Cambridge, England. In the Oct. 1 ASTROPHYSICAL JOURNAL LETTERS Maarten Schmidt of California Institute of Technology in Pasadena, Donald P. Schneider of the Institute for Advanced Study in Princeton, N.J., and James E. Gunn of Princeton University report what--at the time they wrote--was the second, PC 0910 5625, with a redshift of 4.04.
The third, Q0000-26, found by Cyril Hazard of the University of Pittsburgh and Richard McMahon and Mike Irwin of the Institute of Astronomy, has the record-breaking redshift of 4.11. That means we are seeing Q0000-26 as it was when the universe was only a tenth of its present age, or approximately 18 billion years ago if we accept the most widely used value for the age of the universe.
John Webb of ESO has obtained detailed spectra of Q0000-26. Early results from the analysis of these spectra "are causing great excitement among astrophysicists,' says the ESO announcement. These spectra "will permit the investigation of matter in the universe at an earlier time than ever before possible,' says ESO.
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|Date:||Oct 17, 1987|
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