NSF PR 00-29 - May 10, 2000
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Astrophysicists Detect Cosmic Shear, Evidence of Dark
Astrophysicists supported by the National Science Foundation
(NSF) have announced the first observations of cosmological
shear, an effect predicted by Einstein's theory of
relativity. The discovery casts light on the distribution
of the dark matter that makes up much of our universe,
assembling another piece in the cosmological jigsaw
"Pieces of the puzzle are falling into place," said
Morris Aizenman of NSF's Directorate for Mathematical
and Physical Sciences. "Within the first few months
of this millennium, we have solved the riddle of the
geometry of the universe and are now on the threshold
of exploring its structure."
Since it cannot be seen by telescopes, the nature and
distribution of dark matter have puzzled astronomers
for decades. Using the NSF Cerro Tololo Inter-American
Observatory in Chile and a method known as weak gravitational
lensing, the scientists were the first to map the
distribution of dark matter over large swaths of the
The research team included David Wittman, Anthony Tyson
and David Kirkman of Bell Labs, the research and development
arm of Lucent Technologies; Ian Dell'Antonio of NSF's
Kitt Peak National Observatory and Brown University;
and Gary Bernstein of the University of Michigan at
Ann Arbor. Their results will be published in the
May 11 issue of Nature.
Gravitational lensing relies on Einstein's prediction
in his general theory of relativity that gravity bends
light. The team analyzed the light from 145,000 very
distant galaxies for evidence of distortions produced
by the gravitational pull of dark matter that lay
in their paths. To observers, the light from distant
spherical objects is distorted by this gravitational
pull into elliptical shapes, an effect known as cosmic
By analyzing the cosmic shear produced in thousands
of galaxies, the researchers were able to determine
the distribution of dark matter over large regions
of the sky.
"The cosmic shear measures the structure of dark matter
in the universe in a way that no other observational
measurement can," Tyson said. "We now have a powerful
tool to test the foundations of cosmology."
The measurements allowed the astrophysicists to test
current predictions of the ultimate fate of the universe.
According to models favored by cosmologists, the amount
of dark matter helps determine the geometry of the
universe. The researchers were able to rule out a
scenario known as the standard cold dark matter model,
in which there is enough ordinary matter and dark
matter in the universe to eventually stop its expansion
through gravitational force. Measurements of cosmic
shear will enable a comparison of the dark matter
distribution in the late universe with that of the
early universe measured by observations of the cosmic
The team used the Big Throughput Camera, designed and
built expressly to measure cosmic shear, to take images
of 145,000 distant galaxies along three different
lines of sight. The camera was installed in the upgraded
4-meter Blanco telescope at the Cerro Tololo observatory.
Editors: Images will be available on
May 11 at: http://www.bell-labs.com.
See also: http://dls.bell-labs.com.