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PHOTO FILE NO.: STScI-PF95-14
FOR RELEASE: APRIL 5, 1995

HUBBLE VIEWS DISTANT GALAXIES THROUGH A COSMIC LENS

This NASA Hubble Space Telescope image of the rich galaxy cluster,
Abell 2218, is a spectacular example of gravitational lensing. The
arc-like pattern spread across the picture like a spider web is an
illusion caused by the gravitational field of the cluster.

The cluster is so massive and compact that light rays passing through
it are deflected by its enormous gravitational field, much as an
optical lens bends light to form an image. The process magnifies,
brightens and distorts images of objects that lie far beyond the
cluster. This provides a powerful "zoom lens" for viewing galaxies
that are so far away they could not normally be observed with the
largest available telescopes.

Hubble's high resolution reveals numerous arcs which are difficult to
detect with ground-based telescopes because they appear to be so thin.
The arcs are the distorted images of a very distant galaxy population
extending 5-10 times farther than the lensing cluster. This population
existed when the universe was just one quarter of its present age. The
arcs provide a direct glimpse of how star forming regions are
distributed in remote galaxies, and other clues to the early evoution
of galaxies.

Hubble also reveals multiple imaging, a rarer lensing event that
happens when the distortion is large enough to produce more than one
image of the same galaxy. Abell 2218 has an unprecedented total of
seven multiple systems.

The abundance of lensing features in Abell 2218 has been used to make a
detailed map of the distribution of matter in the cluster's center.
From this, distances can be calculated for a sample of 120 faint
arclets found on the Hubble image. These arclets represent galaxies
that are 50 times fainter than objects that can be seen with
ground-based telescopes.

Studies of remote galaxies viewed through well-studied lenses like
Abell 2218 promise to reveal the nature of normal galaxies at much
earlier epochs than was previously possible. The technique is a
powerful combination of Hubble's superlative capabilities and the
"natural" focusing properties of massive clusters like Abell 2218.

The image was taken with the Wide Field Planetary Camera 2.

Credits: W.Couch (University of New South Wales), R. Ellis
(Cambridge University), and NASA


Image files in GIF and JPEG format may be accessed via
anonymous ftp from oposite.stsci.edu in /pubinfo:

GIF: /pubinfo/gif/A2218.gif
JPEG: /pubinfo/jpeg/A2218.jpg

The same images are available via World Wide Web from links in URL
http://www.stsci.edu/public.html.

NOTE TO EDITORS: Requests for a black/white photo or a black/white
35mm slide should be sent via e-mail to "gundy@stsci.edu" or via fax
to 410-338-4579.