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Sharper images: new Hubble camera goes the distance. (This week).

Astronomers have unveiled a picture of the distant universe that ranks as the sharpest and most detailed ever recorded. A faint, red body in that image, taken with a camera that astronauts installed on the Hubble Space Telescope 2 months ago (SN: 3/16/02, p. 163), could be one of the most remote galaxies known, researchers reported April 30 at a NASA press briefing in Washington, D.C.

The new detector, known as the Advanced Camera for Surveys (ACS), outperforms Hubble's workhorse--the widefield and planetary camera 2 (WFPC-2). ACS has twice the field of view as the still-operating WFPC-2 and can detect celestial objects one-fifth as bright and half as large, says ACS lead scientist Holland Ford of Johns Hopkins University in Baltimore.

The showstoppers captured by the new camera include a portrait of the Tadpole, a spiral galaxy that once collided with an intruder and now has a 280,000-light-yearlong streamer of stars and gas. Ford was surprised by the sheer number--about 6,000--of distant, background galaxies dearly recorded in the image.

That's twice the number of background galaxies detected in a landmark set of images--the Hubble Deep Field North--taken from a different, smaller patch of sky by WFPC-2 in 1995. At the time, those images were the most detailed portraits of the early universe (SN: 11/28/98, p. 343).

ACS imaged the 6,000 background galaxies in just one-twelfth the time it took the older camera to observe half as many. Moreover, the new camera captured fainter galaxies, some of them presumably more distant, than those that appear in the deep-field images.

The faint galaxies in the Tadpole image may represent youthful building blocks of modern-day galaxies. After analyzing the brightness of the background galaxies at three different wavelengths, Ford's team estimates that one of the bodies lies some 12.5 billion light-years from Earth. Given the current estimate of the age of the universe (see stow, p. 277), the light now reaching Hubble reveals what the galaxy looked like when the universe was only a billion years old. By staring at a patch of sky for a longer time, ACS can find galaxies that are even more remote, Ford predicts.

Another ACS image shows the collision of two spiral galaxies whose rounded bodies and tails prompted astronomers to dub them the mice. The camera captured the galaxies about 150 million years after they first sideswiped each other, according to computer simulations by Joshua Barnes of the University of Hawaii in Honolulu and John E. Hibbard of the National Radio Astronomy Observatory in Charlottesville, Va. The simulations predict that in about 400 million years, the mice will merge into a single elliptical galaxy. A similar fate may befall our own galaxy, which is expected to collide with Andromeda, its nearest spiral neighbor, several billion years from now.

At the briefing, astronomers reported a second success. An experimental mechanical refrigerator, also installed by astronauts in early March, has revived Hubble's near-infrared camera and multiobject spectrograph, and NASA expects to release images in early June.
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Author:Cowen, R.
Publication:Science News
Article Type:Brief Article
Geographic Code:1USA
Date:May 4, 2002
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