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.
Abell 2218 acts as a powerful lens, magnifying all the galaxies lying behind its core.
These lensed galaxies appear stretched and even multiply imaged.
The new object appears as two thin red streaks inside the circled area.
Image by Jean-Paul Kneib, Richard Ellis and Nasa/Esa
Abell 2218
Abell 2218 is a cluster of galaxies. It is at a distance of about 2 billion light years behind the constellation Draco. This is the 2,218th cluster in George Abell's catalog. It has come under a lot of study recently. When deep images are taken of this cluster, beautiful arcs are seen surrounding the center of the cluster (Abell's images were relatively shallow, so these arcs were not visible to him).
Most of these arcs are actually images from a single galaxy far behind the cluster! When the light from this galaxy (5-10 times more distant than Abell 2218) passes through the cluster, the light gets deflected by the gravitational field the cluster. In this case (which is rare) the light is bent so stronly that the image is sheared out into an arc. Also, because of the strength of the lens, light passing to either side of the cluster gets bent toward the observer and multiple images are seen. Because some of the arcs are blue and some are red, I suspect the arcs may be from more than one background galaxy, perhaps in a cluster or group of their own.
A Democrat telling the truth?
That'll be 10 raps on the knuckles from Sister Mary Yardstick.
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