David Aguilar
(617) 495-7462

Christine Pulliam
(617) 495-7463


CfA Press Release

Release No.: 98-05


WASHINGTON, DC -- How would the Smithsonian Institution's Castle on the National Mall look if it were subject to the same distorting influences of a "gravitational lens" that can warp, disrupt, and multiply the image of an object in space? This computer-distorted image the Castle was presented by Brian McLeod of the Harvard-Smithsonian Center for Astrophysics (CfA), with colleagues from the CfA and the University of Arizona (UA), during a session at the American Astronomical Society meeting here today describingastronomical gravitational lenses seen by the Hubble Space Telescope (HST).

Gravitational lensing is a phenomenon predicted by Einstein's Theory of General Relativity, where light rays emanating from a distant background object, say, a quasar, are bent by the gravitational field of a foreground object, such as a massive black hole or galaxy, thus distorting the appearance of the background object. Researchers from the CfA and UA are using the HST to study some two dozen examples of this phenomenon in a project dubbed "CASTLeS," or, the CfA-Arizona Space Telescope Lens Survey. The results will be used to learn more about the properties of distant galaxies, and to determine the Hubble Constant, i.e., the rate at which the Universe is expanding.

To illustrate gravitational lensing in a more familiar setting, McLeod started with a digitized photograph of the Smithsonian's Castle. He then used computer software originally written for analyzing astronomical gravitational lenses to distort the image as if a black hole with the mass of the planet Saturn lay between the viewer and the Castle. The lensing effect causes each point in the original image to appear twice in the distorted image: once in the outer part of the image; and, once again in the inner part, but now upside down and mirror-reversed. Of course, if there really were a black hole of this size floating above the Mall, the Castle and all its surroundings would be ripped apart by the intense gravitational forces generated by this phenomenon.

The members of the CASTLeS team include, in addition to McLeod, Emilio Falco (CfA), Christopher Impey (UA), Christopher Kochanek (CfA), Joseph Lehar (CfA), Hans-Walter Rix (UA), and Chien Peng (UA).

Images from the CASTLeS project can be found at http://www.cfa.harvard.edu/castles/.

Gravitationallenses occur when the gravitational field of an intervening massiveobject, such as a black hole, bends the light coming from a much moredistant background source. The goal of the CASTLeS project (CfA-ArizonaSpace Telescope Lens Survey) is to study the properties of all the knowncases of galaxies acting as gravitational lenses. To illustrate thedistorting power of lenses, here is what the Smithsonian Institution'sCastle on the Mall in Washington, DC, might look like if an imaginaryblack hole with the mass of Saturn floated down the middle of the NationalMall. (We're ignoring the fact that the gravitational force from such ablack hole would do some serious damage to the Castle and itssurroundings!) Note that there are two images of each part of thebuilding: one inside the circular ring, which has been turned inside out, and one outside. (Computer-enhanced image by BrianMcLeod, Harvard-Smithsonian Center for Astrophysics)

Photo: Smithsonian Institution Archives

For more information, contact:

Brian McLeod, bmcleod@cfa.harvard.edu, 617-495-7023
James Cornell, jcornell@cfa.harvard.edu, 617-495-7462

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