Trent J. Perrotto
Headquarters, Washington
202-358-0321
trent.j.perrotto@nasa.gov
Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-4673
whitney.clavin@jpl.nasa.gov
RELEASE: 11-212
NASA'S SPITZER FINDS DISTANT GALAXIES GRAZED ON GAS
WASHINGTON -- Galaxies once thought of as voracious tigers are more
like grazing cows, according to a new study using NASA's Spitzer
Space Telescope.
Astronomers have discovered that galaxies in the distant universe
continuously ingested their star-making fuel over long periods of
time. This goes against previous theories that galaxies devoured
their fuel in quick bursts after run-ins with other galaxies.
"Our study shows the merging of massive galaxies was not the dominant
method of galaxy growth in the distant universe," said Ranga-Ram
Chary of NASA's Spitzer Science Center at the California Institute of
Technology in Pasadena, Calif. "We're finding this type of galactic
cannibalism was rare. Instead, we are seeing evidence for a mechanism
of galaxy growth in which a typical galaxy fed itself through a
steady stream of gas, making stars at a much faster rate than
previously thought."
Chary is the principal investigator of the research appearing in the
Aug. 1 issue of the Astrophysical Journal. According to his findings,
these grazing galaxies fed steadily over periods of hundreds of
millions of years and created an unusual amount of plump stars, up to
100 times the mass of our sun.
"This is the first time that we have identified galaxies that
supersize themselves by grazing," said Hyunjin Shim, also of the
Spitzer Science Center and lead author of the paper. "They have many
more massive stars than our Milky Way galaxy."
Galaxies like our Milky Way are giant collections of stars, gas and
dust. They grow in size by feeding off gas and converting it to new
stars. A long-standing question in astronomy is: Where did distant
galaxies that formed billions of years ago acquire this stellar fuel?
The most favored theory was that galaxies grew by merging with other
galaxies, feeding off gas stirred up in the collisions.
Chary and his team addressed this question by using Spitzer to survey
more than 70 remote galaxies that existed 1 to 2 billion years after
the big bang (our universe is approximately 13.7 billion years old).
To the surprise of the astronomers, these galaxies were blazing with
what is called H alpha, radiation from hydrogen gas that has been hit
with ultraviolet light from stars. High levels of H alpha indicate
stars are forming vigorously. Seventy percent of the surveyed
galaxies show strong signs of H alpha. By contrast, only 0.1 percent
of galaxies in our local universe possess the signature.
Previous studies using ultraviolet-light telescopes found about six
times less star formation than Spitzer, which sees infrared light.
Scientists think this may be due to large amounts of obscuring dust,
through which infrared light can sneak. Spitzer opened a new window
onto the galaxies by taking very long-exposure infrared images of a
patch of sky called the GOODS fields, for Great Observatories Origins
Deep Survey.
NASA's Jet Propulsion Laboratory in Pasadena manages the Spitzer Space
Telescope mission for the agency's Science Mission Directorate in
Washington. Science operations are conducted at the Spitzer Science
Center. Caltech manages JPL for NASA. For more information about
Spitzer, visit:
-end-
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