Hubble eyes the shape of distant galaxies.

What did galaxies look like when the universe was roughly half its current age? A repaired Hubble Space Telescope has begun to provide the answer.

Hubble's new wide-field and planetary camera now has clearly resolved the shapes of galaxies some 7 billion lightyears from Earth, astronomers reported last week. Because peering at distant galaxies is like looking back in time, the images reveal the galaxy types that existed when the universe was 60 percent of its current age, says Richard Ellis of the University of Cambridge in England.

The abundance of spiral galaxies confirms that galaxies like our Milky Way were well established at this early epoch, he adds. Ellis, who collaborated with Richard E. Griffiths of Johns Hopkins University in Baltimore, presented the new images at a joint meeting of the Royal Astronomical Society and the European Astronomical Society in Edinburgh.

Rather than target specific areas of the sky, the camera observes random patches during times when another Hubble instrument points at a predetermined target. Some of the random images reveal only blank areas of sky, but most show about 20 galaxies, Ellis notes.

Because the survey examines galaxies that evolve in relative isolation, as the Milky Way does, it complements another Hubble project, which analyzes the shapes and colors of distant galaxies that reside in crowded clusters (SN: 12/5/92, p.390). The gravitational forces within a cluster can rip galaxies apart or cause them to collide and merge, dramatically altering the course of galactic evolution. But most galaxies in the cosmos have few close neighbors, comments Ellis.

Comparing images of distant galaxies that grow up in a dense cluster with those that go it alone in the cosmos graphically illustrates the environment's role in galactic evolution, he points out. In addition, Ellis says, the abundance of spiral galaxies relative to ellipticals in the survey of distant, individual galaxies should settle the controversy about whether ellipticals arose from the merger of spirals.

The new Hubble camera has collected images of some 300 galaxies since it joined the survey in February. This amounts to more than 10 times as much survey data as the old wide-field and planetary camera gathered during the past 2 years, Ellis notes. The old camera required much longer exposures and could only image relatively bright galaxies because it lacked the corrective optics to compensate for Hubble's flawed primary mirror. Astronauts replaced the old camera with the new one last December.