Herschel Measures Dark Matter for Star-Forming Galaxies

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Trent Perrotto 202-358-0321
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News release: 2011-057 Feb. 16, 2010

Herschel Measures Dark Matter for Star-Forming Galaxies

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2011-057&cid=release_2011-057

PASADENA, Calif. -- The Herschel Space Observatory has revealed how much dark matter it
takes to form a new galaxy bursting with stars. Herschel is a European Space Agency
cornerstone mission supported with important NASA contributions.

The findings are a key step in understanding how dark matter, an invisible substance permeating
our universe, contributed to the birth of massive galaxies in the early universe.

"If you start with too little dark matter, then a developing galaxy would peter out," said
astronomer Asantha Cooray of the University of California, Irvine. He is the principal
investigator of new research appearing in the journal Nature, online on Feb. 16 and in the Feb. 24
print edition. "If you have too much, then gas doesn't cool efficiently to form one large galaxy,
and you end up with lots of smaller galaxies. But if you have the just the right amount of dark
matter, then a galaxy bursting with stars will pop out."

The right amount of dark matter turns out to be a mass equivalent to 300 billion of our suns.

Herschel launched into space in May 2009. The mission's large, 3.5-meter (11.5-foot) telescope
detects longer-wavelength infrared light from a host of objects, ranging from asteroids and
planets in our own solar system to faraway galaxies.

"This remarkable discovery shows that early galaxies go through periods of star formation much
more vigorous than in our present-day Milky Way," said William Danchi, Herschel program
scientist at NASA Headquarters in Washington. "It showcases the importance of infrared
astronomy, enabling us to peer behind veils of interstellar dust to see stars in their infancy."

Cooray and colleagues used the telescope to measure infrared light from massive, star-forming
galaxies located 10 to 11 billion light-years away. Astronomers think these and other galaxies
formed inside clumps of dark matter, similar to chicks incubating in eggs.

Giant clumps of dark matter act like gravitational wells that collect the gas and dust needed for
making galaxies. When a mixture of gas and dust falls into a well, it condenses and cools,
allowing new stars to form. Eventually enough stars form, and a galaxy is born.

Herschel was able to uncover more about how this galaxy-making process works by mapping the
infrared light from collections of very distant, massive star-forming galaxies. This pattern of
light, called the cosmic infrared background, is like a web that spreads across the sky. Because
Herschel can survey large areas quickly with high resolution, it was able to create the first
detailed maps of the cosmic infrared background.

"It turns out that it's much more effective to look at these patterns rather than the individual
galaxies," said Jamie Bock of NASA's Jet Propulsion Laboratory in Pasadena, Calif. Bock is the
U.S. principal investigator for Herschel's Spectral and Photometric Imaging Receiver instrument
used to make the maps. "This is like looking at a picture in a magazine from a reading distance.
You don't notice the individual dots, but you see the big picture. Herschel gives us the big picture
of these distant galaxies, showing the influence of dark matter."

The maps showed the galaxies are more clustered into groups than previously believed. The
amount of galaxy clustering depends on the amount of dark matter. After a series of complicated
numerical simulations, the astronomers were able to determine exactly how much dark matter is
needed to form a single star-forming galaxy.

"This measurement is important, because we are homing in on the very basic ingredients in
galaxy formation," said Alexandre Amblard of UC Irvine, first author of the Nature paper. "In
this case, the ingredient, dark matter, happens to be an exotic substance that we still have much
to learn about."

NASA's Herschel Project Office is based at JPL, which contributed mission-enabling technology
for two of Herschel's three science instruments. The NASA Herschel Science Center, part of the
Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena,
supports the U.S. astronomical community. JPL is managed by Caltech.

More information is online at http://www.herschel.caltech.edu, http://www.nasa.gov/herschel
and http://www.esa.int/SPECIALS/Herschel/index.html .

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