Oldest galaxy found behind big cluster

Always in the last place you look

Scientists at CalTech may have discovered the most distant object known, and thus the oldest ever seen. If the galaxy, which lies behind the Abell 2218 cluster, is as old as researchers currently think, then the light which has now reached Earth is just 750 million years younger than the universe itself.

The galaxy was identified using the Hubble Space Telescope and the Keck telescopes on Mauna Kau in Hawaii. It is visible thanks to the gravitational lens effect of the Abell 2218 cluster which is so massive that it bends and amplifies the light passing through it, acting as a natural lens in space.

As the universe expands, everything in it moves away from everything else. This causes light to be red shifted; the wavelength of the light increases. The further away an object is, the faster it is receding, and the further redshifted the light is. In this case, the ultraviolet light has been shifted to the infrared.

The astronomers estimate that this object is approximately 2,000 light-years across. This is very small compared with our own galaxy, which is approximately 70,000 light years from centre to tip.

The little galaxy is also forming stars extremely actively. It apparently lacks the typically bright hydrogen emission line, while its ultraviolet light is much stronger than that seen in star-forming galaxies closer by.

"The properties of this distant source are very exciting because, if verified by further study, they could represent the hallmark of a truly young stellar system that ended the Dark Ages," added Dr. Richard Ellis, Steele Professor of Astronomy at Caltech.

"Dark Ages" refers to the time in cosmic history when hydrogen atoms first formed but stars had not yet begun to shine. Nobody is quite clear how long this phase lasted, and the detailed study of the cosmic sources that brought this period to an end is a major goal of modern cosmology.

Hubble may be on borrowed time, but researchers are making sure they get good use out of the time they have left. ®

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