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.
I guess that means that this thing is beyond the farthest know object. That must be really far. But if it is beyond the farthest know object, how do they know it exits?
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.
How fast would that be traveling, with respect to us?
I don't know the formula to convert redshift to recessional velocity offhand, but at a value of z = 7.0, it's more than 90% of "c" for sure.....
Found it.....
v/c = [(z+1)^2 - 1]/[(z+1)^2 + 1]
for z = 7.0. that's equivalent to v/c= 97% of the speed of light.
Thanks.
No charge..... but there will be a pop quiz tomorrow!
BTW, there is no value of z (redshift) for which the recessional velocity is equal to "c." That's because if the emitter were receding from us at v=c, the redshift would be infinite, and the photons would have no wavelength at all! Basically, we can't see anything that's receding that fast (or faster). That's what defines the limit of the visible Universe, the space inside of that limit is known as the Hubble volume.
So, in the limit, as z -> infinity, v -> c.
The gravity from the cluster warps the light from galaxies located behind the cluster. They end up looking like arcs of light. Numerous galaxies beyond the cluster results in numerous arcs and the appearance of a ring.
As Lincoln said, "I can see how it might be possible for a man to look down upon the earth and be an atheist, but I cannot conceive how he could look up into the heavens and say there is no God."
Noticed and was wondering about that object myself. Structurally it appears that it could be two galaxies in collision. But why does it appear so blue? It appears too small to be a foreground object the size of galaxies. If at the distance of the galaxy cluster and appearing that color, it would be in the ultraviolet portion of the spectrum if it were nearby. Curious object.
Another thought: if it is two galaxies in collision, there may be a a burst of star formation activity taking place. Young, massive stars are extremely hot, emitting blue and violet light.
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