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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