Astronomers analyzing the Hubble Deep Field — the faintest view of the universe taken with NASA's Hubble Space Telescope — may have identified what may prove to be the most distant objects observed to date.
Scattered among the nearly 2,000 galaxies in the Hubble images, which were taken last December, researchers at the State University of New York at Stony Brook (SUNY) and collaborators find several dozen galaxies they believe exhibit characteristics which make them appear to be more distant than any seen previously. Six of the galaxies appear to be more distant than the farthest quasars, the current distance record holders. Their results are being published in the June 27 edition of the British science journal Nature.
The candidate galaxies are so far away they may have existed when the universe was less than five percent its present age. If this early galaxy population can be confirmed through further observations, it means that such galaxies would have formed remarkably early in the history of the universe, only a few hundred million years after the Big Bang. The images also give an estimate of how many galaxies were forming at this time in the very early universe.
In one of the first detailed studies of the statistical properties of these distant galaxies, Kenneth Lanzetta and Amos Yahil, of SUNY at Stony Brook, and Alberto Fernandez-Soto, of the University of Cantabria, Spain, have attempted to determine the distance of each of the galaxies based on their colors.
'Since light travels at a finite speed, the galaxies are seen as they were in the distant past, allowing us to study the birth and growth of galaxies versus time,'' says Lanzetta. ''Our results have implications bearing not only on the formation and evolution of galaxies but also on the ultimate fate of the universe,'' adds Yahil.
The team's distance estimates rely on the relationship between speed and distance in the expanding universe. The expansion of the universe causes the light from distant galaxies to be ''redshifted.'' This means that light which leaves a distant galaxy as blue arrives at Hubble as red because of the expansion of space. For a nearby galaxy the shift from blue to red is relatively small, but for a distant galaxy the shift is dramatic, because the light is crossing a larger volume of space.
The researchers took the colors of different kinds of nearby galaxies and redshifted them on the computer to compare with the colors of galaxies observed by Hubble. For each galaxy they assigned a ''most probable'' redshift based on the best match to the ''spectral templates'' they developed.
While the procedure is not definitive for any individual galaxy, the authors contend that it is correct for the majority of galaxies and gives a good overall view of the distribution of distances of the galaxies seen in the Hubble image. If the redshifts are correct, then the light from these galaxies was emitted when the universe was less than one billion years old.
''I am delighted to see the images being used for such studies. The discovery of very high-redshift galaxies is a very provocative result, and extremely interesting if it is right,'' says Harry Ferguson of the Space Science Telescope Institute in Baltimore, MD, a member of the team that obtained the Deep Field Observations. ''It's going to be extremely difficult to confirm, but that will be a high priority for the new infrared camera that is going on the telescope next February.''
The Hubble Space Telescope spent ten days in December 1995 observing a single tiny patch of sky. These observations resulted in the deepest image of the sky, revealing galaxies fainter than had ever been seen before. The striking full-color image of the distant universe was unveiled at the American Astronomical Society Meeting in January 1996, and for the last six months has been the subject of intense study worldwide.
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