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Gravity's lens: Hubble gets sharpest image.



Examining a distant cluster of galaxies cluster of galaxies

Gravitationally bound grouping of galaxies, numbering from the hundreds to the tens of thousands. Large clusters of galaxies often exhibit extensive X-ray emission from intergalactic gas heated to tens of millions of degrees.
, the Hubble Space Telescope Hubble Space Telescope (HST), the first large optical orbiting observatory. Built from 1978 to 1990 at a cost of $1.5 billion, the HST (named for astronomer E. P. Hubble) was expected to provide the clearest view yet obtained of the universe.  has produced the sharpest picture ever of a cosmic mirage called gravitational lensing. Researchers say that as Hubble takes more of these high-resolution images, they will yield a more accurate estimate of the universe's dark matter -- material that can't be observed like ordinary matter.

Richard S. Ellis of Durham University in England and his colleagues weren't searching for a gravitational lens when they began analyzing a Hubble image, taken last November, of a remote galactic cluster galactic cluster: see star cluster.  called AC114. But graduate student Ian Smail spotted two unusual structures on opposite sides of the Hubble picture. The objects were nearly mirror images of each other, indicating that dark matter in the cluster, which lies 4 billion light-years from Earth, acts as a giant lens. The gravity field of the unseen material had bent starlight from a more distant body, much as a distorted glass lens might create multiple images from a single light source.

This gravitational grav·i·ta·tion  
n.
1. Physics
a. The natural phenomenon of attraction between physical objects with mass or energy.

b. The act or process of moving under the influence of this attraction.

2.
 illusion, based on the principle that gravity distorts the path of light, was first proposed by Albert Einstein in 1916, and astronomers have seen the handiwork of gravitational lenses with ground-based telescopes since the late 1970s.

But in previous images, both those captured on the ground and those made by Hubble, the lensed objects appear as blurs. Ellis says that the unprecedented sharpness of the new Hubble picture, which shows L-shaped structures at the edges of the lensed images, enabled him to determine more accurately the concentration and mass of the material in AC114 that acted as a lens. His team has identified a third lensed image of the same distant galaxy in the Hubble photograph, he adds.

Assuming that the gravitational lens coincides with the center of the cluster and obeys similar laws of physics, Ellis calculates that the hidden material has 50 to 100 times the mass of visible material in the cluster and is much more densely concentrated. He reported the findings last week at a press conference in Washington, D.C.

The results match estimates of the amount of dark matter in galactic clusters made by observing lensed images from the ground. But J. Anthony Tyson of AT&T Bell Laboratories in Murray Hill Murray Hill may refer to one of the following places:
  • Murray Hill, Kentucky
  • Murray Hill, Manhattan, a residential neighborhood in New York City
  • Murray Hill, Queens, a different locality in New York City
  • Murray Hill, New Jersey
  • Murray Hill, Pennsylvania
, N.J., likens the impact of Hubble's single set of high-resolution lensed images to the diagnostic power of a single brain scan brain scan
n.
A scintigram of the brain, used to identify cerebral blood flow and to detect intracranial masses, lesions, tumors, or infarcts.
: One or two images may reveal only limited detail. He asserts that the blurrier but far more numerous lensed images seen from Earth still provide the best estimates of the amount of dark matter.

While Ellis disagrees, both scientists say the real revolution in the way astronomers calculate dark matter will come once Hubble begins to record many more gravitationally grav·i·ta·tion  
n.
1. Physics
a. The natural phenomenon of attraction between physical objects with mass or energy.

b. The act or process of moving under the influence of this attraction.

2.
 lensed objects.

Astronomers first postulated the existence of dark matter because the observed mass of the universe is too small to bind large objects gravitationally. The total amount of dark matter may determine the universe's fate -- whether the cosmos has the gravitational power to collapse in on itself or will expand forever.

Ellis notes that the spectra of the lensed galaxy, recorded from Earth, suggest the galaxy lies 8 to 12 billion light-years away.

In a separate report at the press conference, C. Stuart Bowyer bow·yer  
n.
1. One who makes or sells bows for archery.

2. Archaic An archer.
 of the University of California, Berkeley The University of California, Berkeley is a public research university located in Berkeley, California, United States. Commonly referred to as UC Berkeley, Berkeley and Cal , announced that another space-borne observatory, the recently launched Extreme Ultraviolet Explorer Extreme Ultraviolet Explorer: see ultraviolet astronomy. , detected a quasar-like object about 2 billion light-years from Earth. Researchers had thought the observatory would detect few, if any, sources outside our galaxy because of the patchy fog of hydrogen that bathes the stars and absorbs extreme-ultraviolet radiation (SN: 5/23/92, p.344).
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Title Annotation:gravitational lens
Author:Cowen, Ron
Publication:Science News
Date:Oct 17, 1992
Words:601
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