Overfed Black Holes Shut Down Galactic Star-Making

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Whitney Clavin 818-354-4673
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J.D. Harrington 202-358-5241
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News release: 2012-129 May 9, 2012

Overfed Black Holes Shut Down Galactic Star-Making

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2012-129&cid=release_2012-129

PASADENA, Calif. -- The Herschel Space Observatory has shown galaxies with the most
powerful, active black holes at their cores produce fewer stars than galaxies with less active
black holes. The results are the first to demonstrate black holes suppressed galactic star
formation when the universe was less than half its current age.

Herschel is a European Space Agency-led mission with important NASA contributions.

"We want to know how star formation and black hole activity are linked," said Mathew Page of
University College London's Mullard Space Science Laboratory in the United Kingdom and lead
author of a paper describing these findings in this week's journal Nature. "The two processes
increase together up to a point, but the most energetic black holes appear to turn off star
formation."

Supermassive black holes, weighing as much as millions of suns, are believed to reside in the
hearts of all large galaxies. When gas falls upon these monsters, the material is accelerated and
heated around the black hole, releasing great torrents of energy. Earlier in the history of the
universe, these giant, luminous black holes, called active galactic nuclei, were often much
brighter and more energetic. Star formation was also livelier back then.

Studies of nearby galaxies suggest active black holes can squash star formation. The revved-up,
central black holes likely heat up and disperse the galactic reservoirs of cold gas needed to create
new stars. These studies have only provided "snapshots" in time, however, leaving the overall
relationship of active galactic nuclei and star formation unclear, especially over the cosmic
history of galaxy formation.

"To understand how active galactic nuclei affect star formation over the history of the universe,
we investigated a time when star formation was most vigorous, between eight and 12 billion
years ago," said co-author James Bock, a senior research scientist at NASA's Jet Propulsion
Laboratory in Pasadena, Calif., and co-coordinator of the Herschel Multi-tiered Extragalactic
Survey. "At that epoch, galaxies were forming stars 10 times more rapidly than they are today on
average. Many of these galaxies are incredibly luminous, more than 1,000 times brighter than
our Milky Way."

For the new study, Page and colleagues used Herschel data that probed 65 galaxies at
wavelengths equivalent to the thickness of several sheets of office paper, a region of the light
spectrum known as far-infrared. These wavelengths reveal the rate of star formation, because
most of the energy released by developing stars heats surrounding dust, which then re-radiates
starlight out in far-infrared wavelengths.

The researchers compared their infrared readings with X-rays streaming from the active central
black holes in the survey's galaxies, measured by NASA's Chandra X-ray Observatory. At lower
intensities, the black holes' brightness and star formation increased in sync. However, star
formation dropped off in galaxies with the most energetic central black holes. Astronomers think
inflows of gas fuel new stars and supermassive black holes. Feed a black hole too much,
however, and it starts spewing radiation into the galaxy that prevents raw material from
coalescing into new stars.

"Now that we see the relationship between active supermassive black holes and star formation,
we want to know more about how this process works," said Bill Danchi, Herschel program
scientist at NASA Headquarters in Washington. "Does star formation get disrupted from the
beginning with the formation of the brightest galaxies of this type, or do all active black holes
eventually shut off star formation, and energetic ones do this more quickly than less active
ones?"

Herschel is a European Space Agency cornerstone mission, with science instruments provided by
consortia of European institutes and important participation by NASA. NASA's Herschel Project
Office is based at JPL. JPL 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 Caltech, supports the United States astronomical community. Caltech
manages JPL for NASA.

For NASA's Herschel website, visit http://www.nasa.gov/herschel/ . For ESA's Herschel website,
visit http://www.esa.int/SPECIALS/Herschel/index.html .

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