| Einstein Rings - Inside Science
Reported April 2006
BACKGROUND: Astronomers combined two major astronomical projects -- the Hubble Space Telescope and the Sloan Digital Sky Survey -- to discover eight new rings of light, an optical illusion predicted by Albert Einstein. Previously, only three such rings have been observed in visible light.
WHAT CAUSES THE RINGS: "Einstein rings" are an optical illusion created when the fabric of spacetime is warped by the presence of massive objects, like stars or entire galaxies. The effect is known as gravitational lensing and is nature's equivalent to having a giant magnifying glass in space that bends and amplifies the light of more distant objects. Light from a distant galaxy can be deflected by an intervening galaxy to create an arc or multiple separate images. When both galaxies are exactly lined up, the light forms a bulls-eye pattern -- the Einstein ring -- around the foreground galaxy.
GENERAL RELATIVITY BASICS: Albert Einstein proposed his theory of general relativity in 1917. This attributes the force of gravity to the unseen warping of the fabric of spacetime, caused by the presence of mass, or energy. In a 1936 paper, he used general relativity to predict that the gravitational field formed by a massive object could not only warp space and deflect light, but in special cases, the light from a distant object could be so distorted it would create a complete ring.
WHAT WE CAN LEARN: Einstein rings serve as guideposts to help astronomers map the distribution of matter creating the warp in spacetime, and precisely determine the mass of the foreground galaxies. By studying this data, astronomers can glean more knowledge about the unseen dark matter. This is an invisible and exotic form of matter that can't be seen, but its existence can be inferred by measuring its gravitational influence. Dark matter makes up most of the matter in the universe. Astronomers also hope to test the notion that galaxies form from collision, and through mergers of smaller galaxies.
HOW HUBBLE WORKS: Hubble has a long tube that is open at one end, with mirrors to gather and focus light to its "eyes" -- various instruments that enable it to detect different types of light. Light enters the telescope through the opening and bounces off a primary mirror to a secondary mirror, which reflects the light through a hole in the center of the primary mirror to a focal point behind the primary mirror. Smaller mirrors distribute the light to the various scientific instruments, which analyze the different wavelengths. Each instrument uses charge-coupled devices instead of photographic film to capture light -- the same array of photosensitive diodes that are used in digital cameras. The captured light is stored in on-board computers and relayed to Earth as digital signals, and this data is then transformed into images.
The American Astronomical Society and the Space Telescope Science Institute contributed to the information contained in the TV portion of this report.
If you would like more information, please contact:
Dolores Beasley/Erica Hupp
NASA Headquarters
Washington, DC
(202) 358-1753/1237
Donna Weaver
Space Telescope Science Institute
Baltimore, MD
(410) 338-4493
dweaver@stsci.edu
http://www.stsci.edu/
For more information on space science:
American Astronomical Society
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NW Suite 400
Washington, DC 20009-1231
aas@aas.org
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