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Office of News Services
University of Colorado-Boulder
3100 Marine Street, 5th Floor
584 UCB
Boulder, Colorado 80309-0584
(303) 492-6431

Contact:
Brian Keeney, (303) 492-4061, Brian.keeney{at}colorado.edu
John Stocke, (303) 492-1521, Stocke{at}hyades.colorado
Jim Scott, (303) 492-3114

Embargoed until 9:20 a.m. CDT on May 26

TINY GALAXIES ONCE ROARED IN THE UNIVERSE, SAY SCIENTISTS

Astronomers led by the University of Colorado and Carnegie
Observatories have shown that a miniature galaxy less than
one-hundredth the size of the Milky Way is ejecting large quantities
of gas and energy into huge regions of intergalactic space.

"This discovery suggests tiny galaxies that appear very faint and 
dormant today were once much brighter and more active," said
CU-Boulder graduate student Brian Keeney. "It also indicates similar
galaxy systems may have been primarily responsible for the chemical
evolution of the universe in the very early stages of galaxy
evolution," said Keeney, who presented the results of the research at
the American Astronomical Society Meeting held in Nashville, Tenn.,
May 25 through May 29. 

CU-Boulder teamed up with the Carnegie Institution in Washington,
D.C., and East Tennessee State University using the Hubble Space
Telescope and ground-based telescopes to make a series of
observations. Ray Weymann of the Carnegie Institution led a team that
used the electromagnetic spectrum from the brightest quasar in the
sky, 3C273, to discover a dense cloud of gas in the far reaches of
intergalactic space. 

Subsequent observations of the cloud showed it contained elements
formed in stars and ejected into space by supernova explosions, he
said. There was no known source nearby that could have contributed
the ancient elements to this gas.

After several years of searching for the source of this intergalactic 
"pollution", a team led by CU-Boulder Professor John Stocke and
Weymann discovered a tiny "dwarf galaxy" so small that it had been
previously overlooked.

Better images and a detailed spectral analysis obtained by Stocke and 
Keeney at the Apache Point 3.5-meter Telescope in New Mexico showed 
strong evidence that this tiny galaxy was responsible for forming the 
gas cloud.

Some of the strongest evidence is the abundance of elements in the
gas cloud and of the stars in the galaxy match, Keeney said.

In addition, an unusual "overabundance" of the element silicon in the 
gas cloud suggests that thousands of supernovas -- the type created
when massive stars die --were the source of the gas cloud. A spectral
analysis of the dwarf galaxy by Stocke and Keeney showed the dwarf 
galaxy probably experienced a massive "burst" of star formation some
2 billion to 3 billion years ago, and the ejected gas cloud has since
traveled 250,000 light-years to to the location where it is today.

The event may have created thousands of supernovas of the type that 
create the overabundance of silicon, said Keeney. "Two to three
billion years is plenty of time for stars in the 'starburst galaxy'
to die and create supernovas, and for the gas to reach its current
location between us and 3C273.

"Because the large numbers of supernovas made by the dwarf's
starburst blew all of the gas into the surrounding intergalactic
space, there likely will be no further star formation in the galaxy,"
Keeney said. Theoretical models predict the dwarf galaxy will
continue to fade to only about 10 percent of its current brightness.
After another few billion years, the dwarf is expected to be so faint
that it will be comparable to the smallest and faintest galaxies,
known as "dwarf spheroidals."

Not only are these small objects the most numerous of all galaxy
types today, but there also may have been a much larger number of
them in the past, said Stocke. Current theories of galaxy formation
suggest in the early history of the universe, all stars were formed
in tiny galaxies like this one, most of which then merged together
and became incorporated into larger galaxies.

"So our own Milky Way probably was created by mergers of smaller 
galaxies like this one," said Keeney. "If this is correct, and if all 
dwarf spheroidals went through an active starburst phase, a large 
portion of intergalactic space could have been enriched with gas
without any help from more massive galaxies like the Milky Way.

"They may be tiny," Keeney said, "but they are so numerous that their 
collective effects may be more important in the chemical evolution of 
the universe than much larger galaxies like our own."

Project team members include Keeney, Stocke and Kevin McLin of 
CU-Boulder's astrophysical and planetary sciences department, Weymann
of the Carnegie Institution and Professor Mark Giroux of East
Tennessee State University.

Additional observations were made with the Carnegie Institution's Las 
Campanas 2.6-meter telescope in Chile and the Wiyna 3.5-meter
telescope at Kitt Peak, Ariz.

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