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Hubble, Sloan Quadruple Number Of Known Optical Einstein Rings

Date:
November 17, 2005
Source:
Space Telescope Science Institute
Summary:
Astronomers have combined two powerful astronomical assets, the Sloan Digital Sky Survey (SDSS) and NASA's Hubble Space Telescope, to identify 19 new "gravitationally lensed" galaxies. Among these 19, they have found eight new so-called "Einstein rings," which are perhaps the most elegant manifestation of the lensing phenomenon. Only three such rings had previously been seen in visible light.

The thin blue bull's-eye patterns in these eight Hubble Space Telescope images appear like neon sign floating over reddish-white blobs. The blobs are giant elliptical galaxies roughly 2 to 4 billion light-years away. The bulle's-eye patterns are created as the light from galaxies twice as far away is distorted into circular shapes by the gravity of the giant elliptical galaxies. This phenomenon is called gravitational lensing, first predicted by Albert Einstein almost a century ago. The bull's-eye patterns are so-called "Einstein rings," which are the most elegant manifestation of the lensing phenomenon. Einstein rings are produced when two galaxies are almost perfectly aligned, one behind the other. The images were taken between August 2004 and March 2005 with Hubble's Advanced Camera for Surveys. They are part of an ongoing survey, called the Sloan Lens ACS (SLACS) Survey, of about 150 galaxies to hunt for gravitational lenses.
Credit: s: NASA, ESA, and the SLACS Survey Team: A. Bolton (Harvard-Smithsonian CfA), S. Burles (MIT), L. Koopmans (Kapteyn), T. Treu (UCSB), and L. Moustakas (JPL/Caltech)

Astronomers have combined two powerful astronomical assets, the Sloan Digital Sky Survey (SDSS) and NASA's Hubble Space Telescope, to identify 19 new "gravitationally lensed" galaxies. Among these 19, they have found eight new so-called "Einstein rings," which are perhaps the most elegant manifestation of the lensing phenomenon. Only three such rings had previously been seen in visible light.

In gravitational lensing, light from distant galaxies is deflected on its way to Earth by the gravitational field of any massive object that lies in the way. Because of this light bending, we see the galaxy distorted into an arc or multiple separate images. When both galaxies are exactly lined up, the light forms a bull's-eye pattern, called an Einstein ring, around the foreground galaxy.

Besides producing odd shapes, gravitational lensing gives astronomers the most direct probe of the distribution of dark matter in elliptical galaxies. Dark matter is an invisible and exotic form of matter that has not yet been directly observed. By searching for dark matter in galaxies, astronomers hope to gain insight into galaxy formation, which must have started around lumpy concentrations of dark matter in the early universe.

The newly discovered lenses come from an ongoing project called the Sloan Lens ACS Survey (SLACS). A team of astronomers, led by Adam Bolton of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and Leon Koopmans of the Kapteyn Astronomical Institute in the Netherlands, selected the candidate lenses from among several hundred thousand optical spectra of elliptical galaxies in the Sloan Digital Sky Survey.

The team was looking for clear evidence of emission from galaxies twice as far from Earth and directly behind the closer galaxies. They then used Hubble's Advanced Camera for Surveys to snap images of 28 of these candidate lensing galaxies. By studying the arcs and rings produced by 19 of these candidates, the astronomers can precisely measure the mass of the foreground galaxies. These new discoveries add significantly to the approximately 100 gravitational lenses previously known.

"Being able to study these and other gravitational lenses as far back in time as several billion years allows us to see directly whether the distribution of invisible and visible mass changes with cosmic time," says Koopmans. "With this information, we can test the commonly held idea that galaxies form from collision and mergers of smaller galaxies."

The initial findings of the survey will appear in the February 2006 issue of the Astrophysical Journal and in two other papers that have been submitted to that journal.

As Albert Einstein developed his theory of general relativity nearly a century ago, he proposed that the gravitational field from massive objects could dramatically warp space and deflect light. But he thought the effect was unobservable because the optical distortions produced by foreground stars warping space would be too small to ever be measurable by the largest telescopes of his time.

Electronic images and additional information are available at:

http://hubblesite.org/news/2005/32 http://www.slacs.org http://www.arxiv.org/abs/astro-ph/0511453

For information about NASA and agency programs on the Web, visit:

http://www.nasa.gov/home

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. The Space Telescope Science Institute in Baltimore conducts Hubble science operations. The Institute is operated for NASA by the Association of Universities for Research in Astronomy, Inc., Washington. The Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory.


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The above story is based on materials provided by Space Telescope Science Institute. Note: Materials may be edited for content and length.


Cite This Page:

Space Telescope Science Institute. "Hubble, Sloan Quadruple Number Of Known Optical Einstein Rings." ScienceDaily. ScienceDaily, 17 November 2005. <www.sciencedaily.com/releases/2005/11/051117173546.htm>.
Space Telescope Science Institute. (2005, November 17). Hubble, Sloan Quadruple Number Of Known Optical Einstein Rings. ScienceDaily. Retrieved July 24, 2014 from www.sciencedaily.com/releases/2005/11/051117173546.htm
Space Telescope Science Institute. "Hubble, Sloan Quadruple Number Of Known Optical Einstein Rings." ScienceDaily. www.sciencedaily.com/releases/2005/11/051117173546.htm (accessed July 24, 2014).

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