wls@astrovax.UUCP (William L. Sebok) (11/30/84)
I just received this release from Dr. John Huchra of the Center for
Astrophysics. Any comments? We have unofficially known about it here at
Princeton for about a month or two.
Bill Sebok Princeton University, Astrophysics
{allegra,akgua,burl,cbosgd,decvax,ihnp4,noao,princeton,vax135}!astrovax!wls
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NEW GRAVITATIONAL LENS IDENTIFIED: CLOSEST TO EARTH FOUND SO FAR
CAMBRIDGE, Mass. --- A systematic survey of the distances to galaxies has led
to the discovery of a new gravitational lens in the constellation Pegasus which
is apparently serving as a "cosmic magnifying glass" to greatly enhance the
image of a much more distant quasar.
A team of scientists at the Harvard-Smithsonian Center for Astrophysics,
using both conventional instruments and the Multiple Mirror Telescope at the
Smithsonian's Whipple Observatory in Arizona, identified the lens system as a
15th magnitude spiral galaxy on a line directly between the Earth and a
previously unidentified quasar at an apparent distance of 2.3 billion
Megaparsecs (7 billion light years).
According to Einstein's Theory of Relativity, if a suffiently massive object
is positioned between an observer and a distant star, the light from that star
will be deflected, or bent, by the object's gravitational field to form
multiple images.
The first example of such a "multiple quasar" was discovered in 1979, with
subsequent confirmation by the Multiple Mirror Telescope. A concerted search
using the 5-meter Palomar telescope found that the lens was, indeed, a galaxy.
The new lens system (designated 2237+0305) is one of the few examples of the
phenomenon discovered in the past five years, but it is the closest to the
Earth so far found. Relatively nearby at 120 Megaparsecs (4000 million light
years), the lens in only one-tenth as far away as any previously measured
examples, thus promising many opportunities for detailed studies of its
structure and lensing properties.
According to Smithsonian astronomer John Huchra, leader of the research
group, the unusual and near-perfect alignment of this galaxy and quasar form
"a simple lens" system which greatly magnifies the size and brightness of the
quasar.
The lens was initially discovered by observer Edward Horine in late September
during routine spectrographic observations on the Whipple Obbservatory
60-telescope made as part of the ongoing CFA Redshift Program, a deep-sky
survey of the cosmological distances to galaxies in the Northern Hemispere. The
anomalous spectral signature of the combined quasar and galaxy prompted
additional optical observations by Huchra and Graeme Smith using the 4.5-meter
Multiple Mirror telescope, operated jointly by the Smithsonian and the
University of Arizona, and by Stephen Kent using a 24-inch telescope equipped
with an electronic detector. Both observations confirmed that a distant quasar
seemed to be located within only 3/10ths of an arcsecond of the nucleus of the
galaxy.
Many groups, including Smithsonian astronomers, have made concerted efforts
to find additional lenses in the past several years; however, Huchra describes
the chances of finding one aligned with a nearby galaxy as about one in a
million.
Observations by Richard Perley at the Very Large Array of radio telescopes in
Socorro, New Mexico, have detected no radio emission from the lens system.
Preliminary studies also find no x-ray or other high-energy radiation
associated with the source.
Although initial optical observations show only a single image, Huchra
suggests that a tighly grouped cluster of images could exist at a resolution
level beyond the capabilities of the present observations. Larger ground-based
instruments or, in the future, the orbiting Space Telescope, may resolve
additional components.
A paper by Huchra and his collaborators describing the discovery of the new
lens system, together with a description of a model for the lens' magnifying
effects by Marc Gorenstein and Irwin Shapiro of the Center for Astrophysics,
has been submitted to the Astronomical Journal.
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