EMBARGO - For release Monday, 9.20 AM (Central), May 30, 2005

ASTRONOMERS FIND LONELIEST GALAXIES IN THE UNIVERSE

MINNEAPOLIS (May 30, 2005) Astronomers are announcing today that they have discovered a thousand galaxies strewn across the most barren regions of the Universe. These galaxies, found in cosmic voids, are forming stars at a surprisingly high rate, according to Dr Fiona Hoyle of Widener University.

Hoyle made the announcement today at the American Astronomical Society meeting in Minneapolis, Minnesota. The work is a result of a collaboration with Drs Michael Vogeley and Randall Rojas of Drexel University.

Voids are extremely large regions of the universe that are almost empty of matter. Traveling at the speed of light, it would take 100 million years to cross a void. These regions fill around 40\% of the volume of the universe yet contain less than 5\% of the galaxies. While these vast features have been seen since astronomers began to make three-dimensional maps of the universe, early surveys contained only a few voids.

Mapping the deserts of the Universe

Hoyle, Vogeley and collaborators identify their large sample of ``void galaxies'' from a new map of the universe made by the the Sloan Digital Sky Survey (SDSS). Within the volume of the survey lie hundreds of voids. Within each void lie a few void galaxies. Like oases in the desert, these void galaxies light up each void. Digital images and spectroscopy from the SDSS allow astronomers to examine how galaxies in voids differ from their counterparts in groups and clusters.

Finding star formation where it is least expected

Void galaxies appear to be blue in color, which is an indication of recent star formation. If a void galaxy is compared with a galaxy in a denser environment that is of the same type, size and brightness, the one in the void will typically be forming more stars. This is despite the limited amount of gas available in the voids.

``In the highly populated cities people live a frenetic lifestyle where interactions are many. Similarly, galaxies in clusters interact often and during these interactions the galaxies are stripped of their gas'' said Hoyle.

``In contrast, there are a few rugged individuals who, without the competition of others, can live surprisingly well from the meager offerings of the land in the most rural areas. `Void galaxies are few and far between but are still able to form stars at a strong rate as they have held onto their gas supply'' explained Vogeley.

A cosmic gas crisis?

Exactly how a void galaxy uses its gas remains an open question and it depends on how old the galaxies are. The blue color of void galaxies suggests recent star formation, which is more common in younger galaxies. However, structures tend to form earlier in low density regions, if they form at all; gravity quickly empties out void regions. Void galaxies could only be old and appear blue if they used their gas supply in a conservative way and still had gas left to make new stars from.

``In this case void galaxies are like people that wisely saved for retirement so that they had funds at an old age, rather than spending all their money during their youth'' explained Hoyle.

To estimate the age of the void galaxies, Hoyle, Vogeley and collaborators are turning to computer simulations to see under what circumstances voids could form. They are also going to study the properties of the void galaxies using information from observations that are sensitive to gas to try and build the star-formation history of these galaxies. They aim to use these astronomical tests to effectively estimate the galaxy ages to find out when the galaxies formed and how they have been using their gas supply.

``These fascinating results will teach us a lot about how the galaxies formed, though the lesson is hard to read'' said Dr Jim Peebles of Princeton University.

Funding for the creation and distribution of the SDSS Archive 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. The SDSS Web site is http://www.sdss.org/.

The SDSS is managed by the Astrophysical Research Consortium (ARC) for the Participating Institutions. The Participating Institutions are The University of Chicago, Fermilab, the Institute for Advanced Study, the Japan Participation Group, The Johns Hopkins University, the Korean Scientist Group, 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, University of Portsmouth, Princeton University, the United States Naval Observatory, and the University of Washington.

Dr. Fiona Hoyle (215 858 7647, fhoyle@mail.widener.edu)

Dr. Michael S. Vogeley (215 895 2710 vogeley@drexel.edu)

www.physics.drexel.edu/~hoyle/press.html