Overfed Black Holes Shut Down Galactic Star-Making

May 9, 2012

J.D. Harrington
Headquarters, Washington
202-358-5241
j.d.harrington@nasa.gov

Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-4673
whitney.clavin@jpl.nasa.gov

RELEASE: 12-151

OVERFED BLACK HOLES SHUT DOWN GALACTIC STAR-MAKING

WASHINGTON -- 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 the
Nature paper describing these findings. "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 (JPL) 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 the
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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