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Frontiers in Cosmology, Part One
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15035 |
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Section : |
NATURAL SCIENCE
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| Issue
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9 / 1988 |
3,858 Words |
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G. Siegfried Kutter
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Cosmology today is the study of the large-scale structure and evolution of the Universe. To modern scientists, large-scale means that clusters of galaxies are the fundamental units in cosmology, while smaller objects, such as individual galaxies, interstellar clouds, stars, and planets, are the subjects of other branches of astronomy. The Universe of earlier generations of humans was more confined and so were their cosmologies. Their Universe included only the Earth, the Moon, the Sun, the planets, and the fixed stars.
Defined in this historical sense, cosmology may well be the most ancient of all the sciences, yet there seems no end in sight to the discoveries being made in this fascinating field. In fact, the rate of discovery in cosmology has been accelerating during the past few decades. For example, during the past year and a half, three extremely faint and distant objects were discovered, which created a great deal of excitement among professional astronomers. The objects lie at the frontier of space that is observationally accessible with our current generation of instruments and search techniques.
The nearest of these objects is a galaxy discovered by the British astronomer Simon Lilly, working at the University of Hawaii at Manoa. The galaxy cataloged as 0902+34 based on its celestial coordinates, was initially known as just another radio source. However, Lilly has observed this and other similar radio sources since the mid-1980s to see whether optical and infrared counterparts are associated with them. Using several optical telescopes and one of the newly available infrared imaging arrays, which allows for the efficient mapping of the infrared sky, he found an infrared source coincident with the radio source and determined that the emitting object is, in fact, a galaxy. From its spectrum he calculated a redshift of 3.4 (See "The Cosmological Redshift," page 202). This means that the galaxy is receding from us at a speed equal to that of light and is at a distance of roughly 16 billion light-years (LY), making it the most distant galaxy known to date. Previously, the most distant galaxy recorded was at a distance of 13 billion light years.
The second object is a quasar, designated QOO51-279, with a redshift of 4.43 which translates to a recession speed of 110 percent that of light (sic, see page 203) and a distance of about 17 billion LY. It was discovered by a team of astronomers from the Institute of Astronomy in Cambridge, England, and the Kitt Peak National Observatory in Arizona as part of a general quasar search in a 30-square-degree area of the sky centered on the South Galactic Pole. In the December 3, 1987, issue of Nature, S.J. Warren of the Institute of Astronomy and his collaborators report that they used a recently developed multicolor selection technique, which exploits the fact that quasars emit much more ultraviolet radiation than do ordinary galaxies. This permits their detection by digital scanning of multicolor images of the sky. The quasar discovered by the Cambridge-Kitt Peak team is the most distant one known so far and only the sixth with a redshift greater than4. Interestingly, all six of these quasars have been discovered since 1987, three by Warren and his colleagues.
Radiation from the third of the objects on our list is too faint to yield much information, but the extreme shift of its spectrum into the infrared ranged indicates a redshift of approximately 6. This is the greatest redshift of any astronomical object reported to date and corresponds to a recession speed
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