Black holes and galaxies -- Missing link discovered in our own backyard

July 15, 2003

One of the most remarkable discoveries of recent years has been the demonstration that every large galaxy harbors at its core a black hole weighing many million times as much as the Sun, explained research team leader Dr. Guinevere Kauffmann of the Max Planck Institute for Astrophysics in Garching, Germany.

Furthermore, Kauffmann said the mass of this central black hole is very closely related to the properties of the galaxy in which it is embedded. This implies that the formation of the black hole is intimately entwined with that of its galaxy, but the nature of this link remains obscure.

Does the black hole control the growth of its host, or does the galaxy limit the growth of its central black hole? Perhaps black hole and galaxy grow together in some kind of symbiotic relationship? These questions can only be answered by careful study of the growth process, she said.

Co-team leader Dr. Timothy Heckman of the Johns Hopkins University, Baltimore, Md., explained that as black holes grow they release prodigious amounts of energy, in extreme cases outshining their host galaxy to produce a bright quasar. The main epoch of quasar activity, and thus, perhaps, of black hole growth, occurred when the Universe was between a third and a tenth its present age.

Heckman said large galaxies are thought to have formed through the collapse and merging of smaller systems during this same time period. Black hole growth is still detectable in galaxy nuclei today, however, and stars still form in these inner regions. Since nearby galaxies can be studied so much more easily than their distant and more spectacular ancestors, it is no surprise that the link between black hole growth and galaxy growth first became apparent in our own backyard.

By searching for telltale features in the spectra of more than 120,000 galaxies, the SDSS team was able to show that more than 20,000 of them contain black holes that are currently growing.

These growing black holes are located almost exclusively in the more massive galaxies. Massive galaxies where black hole growth is currently weak or absent typically have the structure and star content of old elliptical galaxies as they finished making its stars long ago, the team explained. Galaxies where black hole growth is currently strong have similar mass and structure, but show evidence for substantial recent star formation.

In its conclusions, the team said that as the rate of black hole growth increases, so does the amount of recent star formation. In the most extreme objects the black hole is growing as fast as in bright quasars and the galaxy is dominated by young stars. The stellar mass of these galaxies and the masses of their central black holes are clearly growing together. Like chicken and egg, neither black hole nor galaxy can be said to come first; each is necessary for the other.

ABOUT THE SLOAN DIGITAL SKY SURVEY (SDSS)

The Sloan Digital Sky Survey (sdss.org) will map in detail one-quarter of the entire sky, determining the positions and absolute brightness of 100 million celestial objects. It will also measure the distances to more than a million galaxies and quasars. The Astrophysical Research Consortium (ARC) operates Apache Point Observatory, site of the SDSS telescopes.

SDSS is a joint project of The University of Chicago, Fermilab, the Institute for Advanced Study, the Japan Participation Group, The Johns Hopkins University, the Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, University of Pittsburgh, Princeton University, the United States Naval Observatory, and the University of Washington.
-end-
Funding for the project has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Aeronautics and Space Administration, the National Science Foundation, the U.S. Department of Energy, the Japanese Monbukagakusho and the Max Planck Society.

Authors of the Black Hole findings are:

Guinevere Kauffmann, Max Planck Institute for Astrophysics, Garching, Germany; gamk@mpa-garching.mpg.de
Timothy Heckman, Johns Hopkins University, Baltimore, Md.; heckman@pha.jhu.edu
Christy Tremonti, Steward Observatory, University of Arizona, Tucson, Arizona, tremonti@as.arizona.edu
Jarle Brinchmann, Max-Planck-Institute for Astrophysics, jarle@mpa-garching.mpg.de
Stephane Charlot, Max-Planck-Institute for Astrophysics, charlot@mpa-garching.mpg.de
Simon White, Max-Planck-Institute for Astrophysics, swhite@mpa-garching.mpg.de
Susan Ridgway, Johns Hopkins University; ridgway@pha.jhu.edu
Jon Brinkmann, Apache Point Observatory, Sunspot, NM; brinkmann@nmsu.edu
Masataka Fukugita, University of Tokyo; fukugita@sdss1.icrr.u-tokyo.ac.jp
Patrick B. Hall, Princeton University, Princeton, NJ and the Catholic University of Chile, Santiago; pathall@astro.princeton.edu
Zeljko Ivezic, Princeton University; ivezic@astro.princeton.edu
Gordon Richards, Princeton University; gtr@astro.princeton.edu
Donald Schneider, Pennsylvania State University, State College, Pa.; dps@astro.psu.edu

Max-Planck-Gesellschaft

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