Astronomers have found new galaxies that are the most distant known in the Universe.
One of the goals in deciphering the Universe's past is to see back to the edge of the "Dark Ages," when the first stars and galaxies were being created. Astronomers have taken another step toward that goal with the discovery of new, most distant known galaxies. These are the furthest galaxies yet seen by any optical device.
The Universe was just 500 million years old when the light from these galaxies left. It traveled for more than 13 thousand million years before reaching Earth, where the 10-meter Keck II telescope on Mauna Kea, Hawaii, detected its light. The light of these distant galaxies was amplified by intervening giant galaxy clusters. The use of much nearer massive objects such as galaxy clusters to bend the light of more distant objects is called "gravitational lensing." These clusters act as virtual telescopes in the sky.
The team leader of the project, Richard Ellis of Caltech, describes the phenomenon: "Gravitational lensing is the magnification of distant sources by foreground structures. By looking through carefully selected clusters, we have located six star forming galaxies seen at unprecedented distances, corresponding to a time when the Universe was only 500 million years old, or less than four percent of its present age."
Although this is our farthest back look yet, it is when the Universe was only 300,000 years old that the Dark Ages existed, when no stars were shining. The moment of "cosmic dawn," when the first stars and galaxies began to provide light in the Universe, has yet to be pinpointed. The new information tells us that it was before the Universe reached an age of 500 million years. These galaxies may also have been part of what ended the Dark Ages.
Dan Stark, who detailed the three years of work and new information in his thesis, explains. "Using Keck II, we have detected six faint star-forming galaxies whose signal has been boosted about 20 times by the magnifying effect of a foreground cluster. That we should find so many distant galaxies in our small survey area suggests they are very numerous indeed. We estimate the combined radiation output of this population could be sufficient to break apart (ionize) the hydrogen atoms in space at that time, thereby ending the Dark Ages."
The Spitzer Space Telescope has imaged galaxies that are about 300 to 500 million years older than the new galaxies seen. The galaxies seen by Spitzer had tell-tale signs of old stars. "To produce these old stars requires significant earlier activity," says Stark, "most likely in the fainter star-forming galaxies we have now seen.
