Radio search finds few distant quasars.They lie far away and can reveal what the universe looked like long ago, yet the stars of distant galaxies are often too faint to be seen. In contrast, quasars Proper naming of quasars are by Catalogue Entry, Qxxxx±yy using B1950 coordinates, or QSO Jxxxx±yyyy using J2000 coordinates. This page lists quasars.
As astronomers have used quasars to probe further back in time, they have found that these powerhouses are increasingly scarce beyond a certain dis- tance, referred to as a redshift redshift Displacement of the spectrum of an astronomical object toward longer wavelengths (visible light shifts toward the red end of the spectrum). In 1929 Edwin Hubble reported that distant galaxies had redshifts proportionate to their distances (see of 3. This distance corresponds to a time when the universe was about one-fourth its current age and may mark a sig- nificant epoch in galaxy formation or development, many astronomers speculate. Other researchers find that reasoning flawed. Visible light emitted even by the brightest quasars, if they are extremely remote, can be quenched quench tr.v. quenched, quench·ing, quench·es 1. To put out (a fire, for example); extinguish. 2. To suppress; squelch: by dust lying between those bright bodies and Earth. These researchers argue that a large, unseen population of distant quasars may exist behind intergalactic in·ter·ga·lac·tic adj. Being or occurring between galaxies: intergalactic space. in dust. Now, Peter A. Shaver of the European Southern Observatory European Southern Observatory (ESO), an intergovernmental organization for astronomical research with headquarters in Garching, near Munich, Germany. The ESO began in 1962 as a consortium among Belgium, Denmark, France, Germany, the Netherlands, and Sweden. in Garching, Germany, and his international team of colleagues say they have closed that loophole. By observing quasars at radio wavelengths, a part of the electromag- netic spectrum unaffected by dust, they have confirmed previous findings that the number of quasars starts dwindling dwin·dle v. dwin·dled, dwin·dling, dwin·dles v.intr. To become gradually less until little remains. v.tr. To cause to dwindle. See Synonyms at decrease. beyond a redshift of 3. In particular, although they identified 25 radio-emitting quasars corresponding to the time when the universe was about 20 percent of its current age, they found none representing the period when the universe was half as old. Fewer than 10 percent of all known quasars are strong radio emitters, but Shaver believes they may be representative of the total quasar quasar (kwā`sär), one of a class of blue celestial objects having the appearance of stars when viewed through a telescope and currently believed to be the most distant and most luminous objects in the universe; the name is shortened from population. He and his colleagues report the results of their 4-year study in the Dec. 5 Nature. "It seems that the decline is real, and we are seeing the epoch when quasar activity began," comments Patrick S. Osmer of Ohio State University Ohio State University, main campus at Columbus; land-grant and state supported; coeducational; chartered 1870, opened 1873 as Ohio Agricultural and Mechanical College, renamed 1878. There are also campuses at Lima, Mansfield, Marion, and Newark. in Columbus. The significance of the finding is still open to interpretation, notes Shaver. The era when quasars first began forming may indicate the time when most galaxies began making stars and had concentrated enough matter at their cores to produce quasars. However, if quasars are primarily the product of galactic collisions (SN: 11/23/96, p. 326), then their debut may signal the onset of a later stage of cosmic evolution, when fully formed galaxies began to gather into clusters and merge. |
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