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In search of the oldest galaxies.

In search of the oldest galaxies

Researchers have peered deep into regions of space that appear empty on the most sensitive photographic plates -- and have found those areas to be littered with celestial objects that seem to be galaxies just forming out of the remnants of the Big Bang.

Led by J. Anthony Tyson of AT&T Bell Laboratories in Murray Hill, N.J., the team of U.S. and Canadian scientists began the survey in 1983 to take advantage of the extremely sensitive imaging technology called the charge-coupled device (CCD), a computer-chip-like wafer that nearly allows astronomers to detect individual photons. The "deep CCD survey," published in the July ASTRONOMICAL JOURNAL, found 10 times as many objects as the researchers expected to see, according to Richard Wenk of Bell Laboratories.

Furthermore, the scientists believe these objects are young galaxies just forming. If so, their blue color would be the visible result of a Doppler shift of the ultraviolate light produced by early star formation in the galaxies. According to Wenk, such a redshift would place the galaxies about 12 billion light-years away, which is near most quasars and getting close to the theoretical beginning of the universe 15 billion years ago.

The objects are thought to be the first galaxies to form because the CCDs are theoretically able to see much farther back in the history of the universe than 12 billion years, and there seems to be nothing there in the optical wavelengths. "The implication is that there is nothing to see beyond [these galaxies] that is putting out photons," Wenk says.

Critics say the galaxies the Tyson team is seeing may just be relatively nearby dwarf galaxies, small galaxies that are difficult to see outside of the "local group" that surrounds our own Milky Way. Tyson will be able to prove them wrong only by getting spectra of many of the extremely dim objects and showing that they are in fact very redshifted. This large Doppler redshift could be caused only by light coming from the quickly expanding, you universe.

However, because the very faint light has to be split up to record a spectrum, it is much more difficult to record the spectrum of a dim object than to record the presence of the object itself. Tyson has measured the spectrum of some of the brighter objects and found them to have a fairly large redshift. The implication is that all the objects are the same distance away or farther.

Additional evidence that these objects are actually very distant galaxies lies in the distribution of light within the objects and the wavelength of light that is recorded, says Wenk. "The frequency [of light] is not what you would expect for a dwarf galaxy -- the galaxies we are seeing seem to have an excess of blue, which should only happen when ultraviolet photons are shifted to blue," he says.

Even if the objects are galaxies, there are still not enough of them to account for all the "dark matter" -- the missing mass that astronomers cannot see but think must still exist -- in the universe, says Wenk. Proving the objects are galaxies would, however, give theoreticians a good idea of when galaxies began to form. Tyson's results would put the formation of the first galaxies at about 1 billion years after the Big Bang, and thereafter galaxies would continue to form until about 5 billion years later.

If he is truly seeing galaxies, Tyson can also show that the formation of stars didn't begin all at once, as some theoreticians have speculated. Such a "burst" model would result in a dramatic peak in the number of galaxies at a given age (and therefore redshift). Tyson does not see such a peak.

Wenk says Tyson and his colleagues are now looking at clouds of gas in the same area that may be protogalaxies forming even closer to the beginning of the universe.
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Publication:Science News
Date:Aug 6, 1988
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