Nasa's Hubble Observes Young Dwarf Galaxies Bursting With Stars

[NASA News <hqnews@xxxxxxxxxxxxxxxxxxxxxx>]

Nov. 10, 2011

Trent J. Perrotto 
Headquarters, Washington 
202-358-0321 
trent.j.perrotto@xxxxxxxx 

Donna Weaver/Ray Villard 
Space Telescope Science Institute, Baltimore, Md. 
410-338-4493/410-338-4514 
dweaver@xxxxxxxxx/villard@xxxxxxxxx 

RELEASE: 11-378

NASA'S HUBBLE OBSERVES YOUNG DWARF GALAXIES BURSTING WITH STARS

WASHINGTON -- Using its near-infrared vision to peer 9 billion years 
back in time, NASA's Hubble Space Telescope has uncovered an 
extraordinary population of young dwarf galaxies brimming with star 
formation. While dwarf galaxies are the most common type of galaxy in 
the universe, the rapid star-birth observed in these newly found 
examples may force astronomers to reassess their understanding of the 
ways in which galaxies form. 

The galaxies are a hundred times less massive, on average, than the 
Milky Way, yet churn out stars at such a furious pace that their 
stellar content would double in just 10 million years. By comparison, 
the Milky Way would take a thousand times longer to double its star 
population. 

The universe is estimated to be 13.7 billion years old, and these 
newly discovered galaxies are extreme even for the young universe -- 
when most galaxies were forming stars at higher rates than they are 
today. Astronomers using Hubble's instruments could spot the galaxies 
because the radiation from young, hot stars has caused the oxygen in 
the gas surrounding them to light up like a bright neon sign. 

"The galaxies have been there all along, but up until recently 
astronomers have been able only to survey tiny patches of sky at the 
sensitivities necessary to detect them," said Arjen van der Wel of 
the Max Planck Institute for Astronomy in Heidelberg, Germany, lead 
author of a paper on the results being published online on Nov. 14 in 
The Astrophysical Journal. "We weren't looking specifically for these 
galaxies, but they stood out because of their unusual colors." 

The observations were part of the Cosmic Assembly Near-infrared Deep 
Extragalactic Legacy Survey (CANDELS), an ambitious three-year study 
to analyze the most distant galaxies in the universe. CANDELS is the 
first census of dwarf galaxies at such an early epoch 
. 
"In addition to the images, Hubble has captured spectra that show us 
the oxygen in a handful of galaxies and confirmed their extreme 
star-forming nature," said co-author Amber Straughn at NASA's Goddard 
Space Flight Center in Greenbelt, Md. "Spectra are like fingerprints. 
They tell us the galaxies' chemical composition." 

The resulting observations are somewhat at odds with recent detailed 
studies of the dwarf galaxies that are orbiting as satellites of the 
Milky Way. 

"Those studies suggest that star formation was a relatively slow 
process, stretching out over billions of years," explained Harry 
Ferguson of the Space Telescope Science Institute (STScI) in 
Baltimore, Md., co-leader of the CANDELS survey. "The CANDELS finding 
that there were galaxies of roughly the same size forming stars at 
very rapid rates at early times is forcing us to re-examine what we 
thought we knew about dwarf galaxy evolution." 

The CANDELS team uncovered the 69 young dwarf galaxies in 
near-infrared images taken with Hubble's Wide Field Camera 3 and 
Advanced Camera for Surveys. 

The observations suggest that the newly discovered galaxies were very 
common 9 billion years ago. However, it is a mystery why the newly 
found dwarf galaxies were making batches of stars at such a high 
rate. Computer simulations show star formation in small galaxies may 
be episodic. Gas cools and collapses to form stars. The stars then 
reheat the gas and blow it away, as in supernova explosions. After 
some time, the gas cools and collapses again, producing a new burst 
of star formation, continuing the cycle. 

"While these theoretical predictions may provide hints to explain the 
star formation in these newly discovered galaxies, the observed 
bursts are much more intense than what the simulations can 
reproduce," van der Wel said. 

The James Webb Space Telescope, an infrared observatory scheduled to 
launch later this decade, will be able to probe these faint galaxies 
at an even earlier era to see the glow of their stars, reveal their 
chemical composition, and offer better details on their formation. 

The Hubble Space Telescope is a project of international cooperation 
between NASA and the European Space Agency. Goddard manages the 
telescope. STScI conducts Hubble science operations and is operated 
for NASA by the Association of Universities for Research in Astronomy 
Inc. in Washington. 

For images and more information about Hubble and the CANDELS results, 
visit: 

http://www.nasa.gov/hubble 

	
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