Mirages in the Sky Probe Dark Matter in the Universe
Scientists from the Sloan Digital Sky Survey project (SDSS) announced today two intriguing discoveries relating to the phenomenon of gravitational lenses.
"We have discovered that a system appearing to consist of four separate quasars—the most luminous class of objects in the universe—actually contains four mirages of just one quasar," says Donald Schneider, professor of astronomy and astrophysics at Penn State and a member of both SDSS discovery teams. Schneider also is the chair of the SDSS Quasar Science Group and its coordinator of scientific publications.
Albert Einstein's Theory of General Relativity predicts that the gravitational pull of a massive body can act as a lens, bending and distorting the light of a distant object. A massive structure located between a distant quasar and Earth can "lens" the light of the quasar, making the image substantially brighter and producing several mirage images from the one object. "The image of this quasar is being split into four copies and projected onto the sky at the largest image separation ever recorded," Schneider explains. "This lensing must be caused by an unexpectedly large amount of dark matter that is invisible to us on Earth." This discovery is detailed in the current issue of the journal Nature, published on 18 December.
In the second paper, to be published in the Astronomical Journal in March 2004, an SDSS team used the high resolution of the Hubble Space Telescope to examine four of the most distant known quasars—located as far back in time as astronomers have been able to see objects—for signs of gravitational lensing. "Theories predict that a large fraction of the most distant quasars should be mirages because a massive lensing object is more likely to exist between them and the Earth," Schneider explains. These theories help to explain how such luminous objects could have formed so early in the history of the universe. High luminosity at a great distance generally requires a violent clash of large amounts of matter with a large black hole in order to create fireworks colossal enough to be seen on Earth. "If the observed brightness of distant quasars were significantly boosted by the magnification of a gravitational lens, the quasars' black holes could be of modest size, which would remove the requirement that very massive black holes formed when the universe was so young," Schneider explains. "But when we examined the Hubble Space Telescope images of four of the most distant known quasars, we were quite surprised to find that not even one of them shows any evidence of gravitational lensing; therefore, the supermassive-black-hole issue remains a puzzle."
Gordon Richards, a former Penn State postdoctoral scholar, also is a member of both SDSS teams that made these discoveries.
FOR MORE INFORMATION:
The full text of a press release from the Sloan Digital Sky Survey can be found on the web at http://www.sdss.org
ILLUSTRATION:
http://www.sdss.org/news/releases/20031217.lensing.html
ILLUSTRATION CAPTION:
A new gravitational lens discovered by the Sloan Digital Sky Survey. The detailed picture, taken by the Subaru Telescope on the summit of Mauna Kea in Hawaii, shows four images of the same quasar (the four white dots in the center). The quasar is almost 10 billion light years from us and its light has been split into four by the gravitational influence of a foreground cluster of galaxies, "only" 6.2 billion light years away. Some of the galaxies of the cluster appear as yellow dots on the image. [Credit: Sloan Digital Sky Survey]
CONTACTS AT PENN STATE:
- Donald P. Schneider, dps@astro.psu.edu , 814-863-9554
- Barbara K. Kennedy (PIO), science@psu.edu , 814-863-4682
OTHER SDSS CONTACTS:
- Masamune Oguri, University of Tokyo,
oguri@utap.phys.s.u-tokyo.ac.jp, 81-3-5841-4177
- Naohisa Inada, University of Tokyo, Japan,
inada@utap.phys.s.u-tokyo.ac.jp, 81-3-5841-4177
- Gordon T. Richards, Princeton University Observatory,
gtr@astro.princeton.edu, 609-258-7529
- Michael A. Strauss, SDSS Scientific Spokesman,
strauss@astro.princeton.edu, 609-258-3808
- Gary S. Ruderman, (PIO), Sloan Digital Sky Survey, sdsspio@aol.com,
312-320-4794
ABOUT THE SLOAN DIGITAL SKY SURVEY (SDSS):
The Sloan Digital Sky Survey (http://www.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, the Fermi National Accelerator Laboratory, 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. 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.
PAPERS DISCUSSED IN THIS RELEASE
"A Gravitationally Lensed Quasar with Quadruple Images Separated by 14.62 Arcseconds" ( Nature , December 18/25 issue)
The paper proposed for the March 2004 issue of the Astronomical Journal, titled "A Snapshot Survey for Gravitational Lenses Among z >= 4.0 Quasars: I. The z > 5.7 Sample," (The Astronomical Journal, March 2004 issue). A copy of this paper can be found at http://arxiv.org/abs/astro-ph/0309274.