Heavenly bodies make their UV film debut.

Heavenly bodies make their UV film debut

When the space shuttle Columbia landed last month after a nine-day research mission called Astro, one anxious scientist still didn't know if his shuttle-borne experiment had worked. Theodore P. Stecher of NASA's Goddard Space Flight Center in Greenbelt, MD., had to retrieve and develop 900 frames of ultraviolet-sensi-tive film from the payload before he could assess the success of the Ultraviolet Imaging Telescope, the mission's sole picture-taking instrument.

Last week, at the American Astronomical Society meeting in Philadelphia, Stecher announced that the telescope had performed well indeed, and he presented several images to prove it.

The central region of the globular cluster Omega Centauri (pictured here) occupies a region of the Milky Way some 17,000 light-years from Earth and houses nearly a million stars. Until now, none of those stars had been photographed in the ultraviolet. Optical pictures of the cluster, taken by ground-based telescopes, detect mainly red giant stars and yellow main-sequence stars, whereas the ultraviolet image primarily spotlights hotter, less common stars that evolved from red giants by ejecting their outer atmosphere.

Stecher points out that the ultraviolet photograph, in contrast to optical images, does not show a strong concentration of stars at the very center of the cluster. Whether the apparent dark areas or "holes" in the core represent light-obscuring dust clouds, stars too din to detect or an actual gap in the cluster remains unclear, says Goddard astronomer Susan G. Neff.

Neff notes another curious feature: an unusually large variation in stellar light intensity, indicated by the presence of several different hues in the false-color image. She says that Omega Centauri may have collided at some earlier time with another cluster to create the mix of ultraviolet intensities and the lower-than-expected core density apparent in the globular cluster today.

The Ultraviolet Imaging Telescope also captured on film the spiral galaxy M81, about 12 million light-years from Earth. Bright spots int he galaxy's curving arms reveal areas where starbirth concentrates. Some of these bright regions form a ring -- barely visible in optical images of M81 -- about 19,500 light-years from the galactic center. Neff suggests that gravitational pull from another galaxy that passed nearby, perhaps the irregular galaxy M82, could have helped form the ring-shaped feature.