Astronomers using the largest optical and infrared telescopes in theworld have found the most distant known object in the cosmos, a younggalaxy in existence when the universe was only 6 percent of its presentage, and nearly 90 million light-years farther than any previously discovered.
The serendipitous discovery is raising realistic hopes that theemerging generation of large ground-based telescopes will unveilthe formative stages of galaxies, allowing astronomers to resolvetwo of the central questions facing contemporary astrophysics:How and when did galaxies form?
The findings will be detailed in a scientific paper to be published in anupcoming issue of the Astrophysical Journal Letters. The paper was written byArjun Dey, a Hubble Postdoctoral Fellow at The Johns Hopkins University,astronomers Hyron Spinrad, Daniel Stern and James R. Graham at the Universityof California, Berkeley, and Frederic H. Chaffee at the W.M. Keck Observatoryin Hawaii.
"It is an extremely exciting discovery, since so little is knownabout this stage of the universe, in terms of the objects that livedthere, or how galaxies -- giant collections of stars -- might form," Dey said.
"We are trying to find baby galaxies. These are galaxies that wouldeventually turn into something like the one we live in, but wouldbe undergoing their first episode of star formation. In other words ... theyare essentially collapsing from a large gas cloud and forming their firstgeneration of stars."
Because of its great distance and the constant speed of light, astronomers nowsee the galaxy as it was when the universe was only 6 percent of its presentage, about 820 million years after the Big Bang. Astrophysicists need toobserve embryonic galaxies to test, refine and/or refute theories about howgalaxies form. Without direct, observational evidence, specific theoriescannot be substantiated.
"The problem is that, although people have looked for many, many years, theyhave never been able to find galaxies that are truly primeval," said Dey.
Astronomers don't yet know whether they have now discovered one such primevalgalaxy, but it is their best candidate to date. Scientists can determine thedistance to a galaxy by measuring the speed with which it is moving away fromus as the universe expands. More distant galaxies are receding faster, aphenomenon observed in the late 1920s by American astronomer Edwin Hubble.The faster a galaxy is moving, the more its light is shifted to the longer (orredder) wavelengths. The light is said to be "red shifted."
The farther away a galaxy is, the faster it appears to be receding from us,and the greater its redshift. The newly discovered galaxy, called 0140+326RD1(or RD1), has a redshift of 5.34, marking the first time the 5.0 redshiftbarrier has been broken.
"We've never had any glimpse of what might be at redshifts beyond 5," saidDey, the team leader. "But now that we know what to look for, I'm sure thisrecord will be broken in a matter of months."
The astronomers discovered RD1 while they were observing distant galaxies withthe 10-meter Keck II Telescope located atop Mauna Kea, a dormant volcano onthe Big Island of Hawaii. Keck II is an identical twin to the 10-meter Keck I;they are the largest optical and infrared telescopes in the world. InSeptember 1997, Dey, Spinrad, Stern and Graham were using the KeckLow-Resolution Imaging Spectrograph to analyze the light from a very distantand faint galaxy in the constellation of Triangulum, when they spottedsomething unexpected: the spectral signature of another even fainter galaxywhich had not been seen on existing images of that patch of sky.
In December, the team took deeper images by increasing the exposure time oftheir observations. "And sure enough, we began to see something show up: afaint blob," Dey said. Keck Observatory director Frederic Chaffee joined theteam, and they studied the object's light again, confirming the discovery ofthe new, extremely distant galaxy. The astronomers are continuing follow-upobservations with Keck, and they hope to observe the object with the HubbleSpace Telescope.
"Astronomers the world over have spent years devising clever techniques tofind galaxies beyond redshift 5, but so far have come up empty," said Chaffee,who has watched numerous teams search for such ultra-distant objects. "We hadassumed this was because such objects are extremely rare and faint -- ratherlike seeking out the needle in a 10,000,000-straw haystack. But here,one was found serendipitously by observing only one tiny area of sky."
The previous most-distant known object was a galaxy at redshift 4.92,discovered by astronomers using the Keck and Hubble telescopes.
"How galaxies formed in the early universe is one of the most exciting puzzlesin astronomy today," said Hugh Van Horn, director of the National ScienceFoundation's Division of Astronomical Sciences. "This record-breakingobservation will give us new information about a galaxy in its youth."
The actual age of the universe is a matter of debate. However, if astronomersuse 13 billion years as the age of the universe, then light from RD1 wasemitted when the universe was 820 million years old. The light has traveled adistance of about 12.22 billion light-years. The previous most-distant galaxyis about 12.13 billion light-years from Earth, nearly 90 million light-yearscloser than RD1.
RD1 is a fairly average galaxy, with a mass and luminosity less than that ofthe Milky Way, Dey said. That finding gives astronomers hope that theembryonic stages of galaxies similar to today's large spiral and ellipticalgalaxies might be bright enough to be seen with greater ease by the Kecks andother large telescopes now being built.
Presently, the two 10-meter Keck telescopes are unrivaled. But within adecade, about a dozen 8-meter class telescopes will join the hunt for answersto some of the most pressing questions facing cosmology today.
"We are sort of at a watershed in observational cosmology, in terms ofunderstanding how galaxies form and evolve," Dey said.
The astronomers hope to find other primeval galaxy candidates ateven larger distances. "Deep targeted searches with the new generationof large ground-based telescopes will soon uncover more nascent galaxies,"said Spinrad.
The Hopkins/UC-Berkeley/Keck research has been funded by NASA and the NationalScience Foundation.
Note: An image showing the area of the sky containing the galaxycan be downloaded at the following Web address:http://www.jhu.edu/news_info/news/home98/mar98/images/stellar.gif
A print of the image also is available to reporters by contacting Emil Venereat the phone number and e-mail address listed at the top of thisrelease. Other media contacts for this story are Bob Sanders, atUC-Berkeley, (510) 643-6998, ([email protected]), andAndrew Perala, at the W.M. Keck Observatory, (808) 885-7887([email protected]).
The above story is based on materials provided by Johns Hopkins University. Note: Materials may be edited for content and length.
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