Posted on 02/15/2004 1:42:33 PM PST by concentric circles
Peering back in time to when the universe was just 750 million years old, a team of astrophysicists announced Sunday they have spied a tiny galaxy that is the most farthest known object.
"We are confident it is the most distant known object," California Institute of Technology astronomer Richard Ellis said of the galaxy, which lies roughly 13 billion light-years from Earth.
The team uncovered the faint galaxy using the two most powerful telescopes of their kind – one in space, the other in Hawaii – aided by the natural magnification provided by a massive cluster of galaxies.
The gravitational tug of the cluster, called Abell 2218, deflects the light of the far more distant galaxy and magnifies it many times over.
"Without the magnification of 25 afforded by the foreground cluster, this early object could simply not have been identified or studied in any detail with presently available telescopes," said astronomer Jean-Paul Kneib, of Caltech and the Observatoire Midi-Pyrenees in France.
The magnification process, first proposed by Albert Einstein and known as "gravitational lensing," produces double images of the galaxy.
Word of the discovery came during the annual meeting of the American Association for the Advancement of Science in Seattle. Further details appear in a forthcoming issue of the Astrophysical Journal.
The discovery gives a rare glimpse of the time when the first stars and galaxies began to blink on, ending a period that cosmologists call the "Dark Ages," said Robert Kirshner, an astronomer with the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.
"The possibility is here we really are beginning to peek into that time," said Kirshner, who was not connected with the discovery.
"People have gone there in their imagination – they've thought about it. Now we are getting the facts. And there's nothing like getting the facts," he added.
The Hubble Space Telescope revealed the first glimpse of the galaxy, backed up by subsequent observations made with the Keck Observatory's 10-meter telescopes atop Mauna Kea.
The galaxy is just 2,000 light-years across. That's far smaller than our own Milky Way, which is roughly 100,000 light-years in diameter.
Analysis of the galaxy revealed its light had been shifted into redder wavelengths, or redshifted. The farther away an object is in our expanding universe, the faster it is moving and the larger its redshift.
The team was less confident about the precise redshift they had measured, estimating it as between 6.6 and 7, Ellis said. Any value in the range would still place the galaxy as the farthest known object, he added.
The galaxy also has a stronger ultraviolet signal than that seen in younger star-forming galaxies. That suggests the galaxy contains a higher proportion of massive stars.
Cosmologists have predicted that early galaxies contained types of stars unlike those that came into being much later in the history of the universe.
The team searched only a small area of the sky before they turned up the galaxy, suggesting the sky is dense with similar galaxies and that the type of massive stars it contains were common after the end of the so-called Dark Ages, Ellis said.
"That's very interesting if it's true," Kirshner said.
No one knows how long the Dark Ages lasted in the wake of the Big Bang 13.7 billion years ago.
The Universe is fantastically complex ... but it is not ridiculous.
A universe has gotta know its limitations.
-- Modified saying from Dirty Harry
"The researchers acknowledge that while several lines of evidence point to an extremely young age for this galaxy, they don't have spectroscopic signatures that many would consider the "smoking gun." "
"Such unambiguous spectroscopic evidence is difficult to get at these distances and with current technology, acknowledges Massimo Stiavelli, an astronomer with the Space Telescope Science Institute in Baltimore who was not part of the team. Still, he adds, the group's evidence "is reasonably convincing."
"Dr. Kneib notes that his team had to overcome skepticism that they could achieve their goal when they first applied for telescope time. But now that the results are out - and to be published in an upcoming edition of the Astrophysical Journal - the team hopes to get more time to study the object, as well as to search for counterparts elsewhere in the sky."
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