Whitney Clavin/Jane Platt 818-354-4673/354-0880

Jet Propulsion Laboratory, Pasadena, Calif.

News Release: 2006-101 August 23,
2006

NASA Galaxy Hunter: Huge Black Holes Stifle Star Formation

Supermassive black holes in some giant galaxies create such a hostile
environment, they shut down the formation of new stars, according to
NASA Galaxy Evolution Explorer findings published in the August 24
issue of Nature.

The orbiting observatory surveyed more than 800 nearby elliptical
galaxies of various sizes. An intriguing pattern emerged: the more
massive, or bigger, the galaxy, the less likely it was to have young
stars. Because bigger galaxies are known to have bigger black holes,
astronomers believe the black holes are responsible for the lack of
youthful stars.

"Supermassive black holes in these giant galaxies create unfriendly
places for stars to form," said Dr. Sukyoung K. Yi of Yonsei University
in Seoul, Korea, who led the research team. "If you want to find lots
of young stars, look to the smaller galaxies."

Previously, scientists had predicted that black holes might have dire
consequences for star birth, but they didn't have the tools necessary
to test the theory. The Galaxy Evolution Explorer, launched in 2003, is
well-suited for this research. It is extremely sensitive to the
ultraviolet radiation emitted by even low numbers of young stars.

Black holes are monstrous heaps of dense matter at the centers of
galaxies. Over time, a black hole and its host galaxy will grow in
size, but not always at the same rate.

Yi and his collaborators found evidence that the black holes in
elliptical galaxies bulk up to a critical mass before putting a stop to
star formation. In other words, once a black hole reaches a certain
size relative to its host galaxy, its harsh effects become too great
for new stars to form. According to this "feedback" theory, the growth
of a black hole slows the development of not only stars but of its
entire galaxy.

How does a black hole do this? There are two possibilities. First, jets
being blasted out of black holes could blow potential star-making fuel,
or gas, out of the galaxy center, where stars tend to arise.

The second theory relates to the fact that black holes drag surrounding
gas onto them, which heats the gas. The gas becomes so hot that it can
no longer clump together and collapse into stars.

Other authors of this research include: Drs. Kevin Schawinski, Sadegh
Khochfar and Sugata Kaviraj of the University of Oxford, England; Dr.
Young-Wook Lee of Yonsei University in Seoul, Korea; Drs. Alessandro
Boselli, Jose Donas and Bruno Milliard of the Laboratory of
Astrophysics of Marseille, France; Tim Conrow, Drs. Tom Barlow, Karl
Forster, Peter G. Friedman, D. Chris Martin, Patrick Morrissey, Mark
Seibert, Todd Small and Ted K. Wyder of the California Institute of
Technology in Pasadena; Dr. Susan Neff of NASA's Goddard Space Flight
Center, Greenbelt, Maryland; Dr. David Schiminovich of Columbia
University, N.Y.; Drs. Tim Heckman, Alex Szalay and Luciana Bianchi of
Johns Hopkins University, Baltimore, Md.; Dr, Barry Madore of the
Observatories of the Carnegie Institute of Washington in Pasadena; and
Dr. R. Michael Rich of the University of California, Los Angeles.

Additional information about Galaxy Evolution Explorer is online at
http://www.galex.caltech.edu .

The California Institute of Technology in Pasadena, Calif., leads the
Galaxy Evolution Explorer mission and is responsible for science
operations and data analysis. NASA's Jet Propulsion Laboratory, also in
Pasadena, manages the mission and built the science instrument. The
mission was developed under NASA's Explorers Program managed by the
Goddard Space Flight Center, Greenbelt, Md. Researchers from South
Korea and France collaborated on this mission.