Astronomers Find Thousands of New Galaxies

A false-color mosaic of the Coma cluster reveals thousands of new faint objects (green), many of which belong to the cluster. The mosaic combines visible-light data from the Sloan Digital Sky Survey (color coded blue) with long- and short-wavelength infrared views (red and green, respectively) from NASA's Spitzer Space Telescope. Credit: NASA/JPL-Caltech/GSFC/SDSS

More than a thousand previously unknown dwarf galaxies have been detected in the Coma cluster of galaxies 320 million light-years away by NASA's Spitzer Space Telescope.

Though tiny compared to bigger galaxies, dwarf galaxies play a crucial role in cosmic evolution. Astronomers think they were the first galaxies to form, providing the building blocks for larger galaxies. They're also the most numerous type of galaxies around: Computer simulations, in fact, suggest that giant clusters of galaxies should contain more dwarf galaxies than astronomers have observed.

To find the thousands of "missing" galaxies, astronomers at NASA's Goddard Space Flight Center in Greenbelt, Maryland, stitched together 288 individual exposures from the Spitzer Space Telescope. Each exposure lasted 70 to 90 seconds, forming a large mosaic covering 1.3 square degrees of sky when combined with the image data from the Sloan Digital Sky Survey. Though a small chunk of the sky, the team found almost 30,000 new objects in a relatively short period of time.

To the team's surprise, many of the new objects turned out to be Coma galaxies, not galaxies beyond the cluster. Leigh Jenkins, a GSFC astronomer, estimates that about 1,200 of the faint objects are dwarf galaxies-many more than have been previously identified.

"We have suddenly been able to detect thousands of faint galaxies that weren't seen before," Jenkins said. Her team's study of the Coma cluster is detailed in a recent issue of the Astrophysical Journal.

How can astronomers see such faint galaxies? The universe emits a wealth of visible light, which allows us to se stars with an unaided eye. But most of the light from space is invisible to humans-which is why telescopes like Spitzer that can "see" infrared light help astronomers make new discoveries in well-studied parts of the cosmos.

The team may have found thousands of new objects, but additional Coma dwarf galaxies might be lurking in the Spitzer telescope data, the team said. By using telescopes that can see even "deeper" into the cosmos, the astronomers are currently trying to find out how many of the faintest objects belong to the Coma cluster.

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