Within a galaxy and outside a supernova.

Within a galaxy and outside a supernova

Astronomers got more than they expected when they turned the Hubble Space Telescope on the galaxy NGC 7457, about 40 million light-years away. "We thought it would be a boring, ordinary galaxy," says Tod R. Lauer of the National Optical Astronomy Observatories in Tucson, Ariz.

Instead, hubble's wide-field and planetary camera found a galactic center packed with about 400 times more stars than predicted from Earth observations. The left image shows NGC 7457's center, while the right image, with contrast adjusted, reveals a huge concentration of stars at the galaxy's heart.

The finding, announced last week, suggests that the centers of many "normal" galaxies may contain far more stars than previously believed. It also raises the question of whether the crowd of stars in NGC 7457 results from the gravitational attraction of a black hole at its center.

"We're not claiming that this is a black hole," says Hubble program scientist Edward Weiler of NASA. "It is not inconsistent with a black hole, however."

Hubble's faint-object camera, provided by the European Space Agency, also photographed a bright ring or shell of gas surrounding supernova 1987A. Both ground-based and satellite observations had indicated the existence of the material, a slowly moving remnant of the hydrogen-rich envelope ejected by the star during its red envelope ejected stage, some 10,000 years before it exploded.

A few hours after the cataclysmic blast, ultraviolet radiation from the supernova heated the gas and set it aglow. Within a few decades, astronomers say, fast-moving debris from the explosion will completely engulf the gas.