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Faint But Distant Galaxies Spotted Using Space Lens Trick
By Heather Sparks
SPACE.com Staff Writer
posted: 09:00 am ET
05 October 2001
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hubble_lensing_011005A team of international astronomers announced Friday that they had spotted some of the most distant small and relatively low-luminosity galaxies ever seen. According to the space-time continuum, the oldest galaxies in existence are also the farthest away. To view them today is to see them as they existed nearly billions of years ago, shortly after the universe was born. The oldest points of light in the universe are, therefore, the small building blocks of today's larger galaxies and galaxy clusters, according to the leading theories of galactic evolution. "To view them is to travel back in time and see how galaxies assembled," explained Richard Ellis, a Caltech astronomy professor. Ellis and an international team of astronomers collaborated to find these far-off objects with the help of the space-based Hubble Space Telescope and the Keck telescopes in Hawaii. The team has so far discovered three proto-galaxies, the building blocks of larger galaxies, using a technique called gravitational lensing. The technique takes advantage of the gravitational pull of immense galaxy clusters that block a direct view of the very far, very faint proto-galaxies. The gravity of the massive intervening objects serves as a magnifying glass, actually bending and magnifying the light of the farther-afield object, making it visible. The farthest and oldest, and therefore according to Ellis, "the most interesting" proto-galaxy was found to be 11.4 billion light-years behind the galaxy cluster Abell 2218, itself two billion light-years away. The cluster is a grouping of galaxies that has a mass equal to that of ten thousand galaxies. "The system contains about a million or so stars at a distance of 13.4 billion light-years, assuming that the universe is 14 billion years old," Ellis said. More distant galaxies and quasars -- large, extremely bright galaxies with supermassive black holes at their centers -- have been found by conventional means, but the newly found galaxies are important because they are small and do not shine so brightly.The light of the proto-galaxy was magnified more than 30 times by Abell 2218. The Hubble image showed the galaxy's light split into two images because of Abell's uneven distribution of matter. The light was essentially pulled in two directions. The tiny, more distant galaxy is only 5 light-years across, just one-twentieth the size of our Milky Way Galaxy. Studying objects as old as this one, Ellis said, will tell astronomers how the universe has evolved. "We think there was only dark matter in the universe and it acted like a seed for the growth of galaxies. It's like how dust gathers a raindrop," Ellis said. "When the universe was a billion years-old, hydrogen began clumping around dark matter and the gas slowly began cooling. Finally it collapsed around the dark matter and at that point hydrogen began to burn and produced the strong spectrum line that is now seen by the Keck [telescopes]." The discovery is being reported in an upcoming issue of the Astrophysical Journal. More About Deep Space Objects: Astronomy News by TopicThis Week in Science & Astronomy: News Briefs
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