Imagine two neutron stars colliding, or even worse, a neutron star and a black hole. The release of energy would be catastrophic, and has apparently now led to the first detection in visible light from a short gamma-ray burst. Thus we're beginning to get a handle on the most powerful explosions in the known universe, whose identity has bedeviled astronomers for thirty years. There are actually two different kinds of gamma-ray bursts. The longer ones have been linked to the explosion of a massive star as it collapses into a black hole. It's the short-duration bursts that have proven the greater challenge. The new work, performed at La Silla (Chile) and at the European Southern Observatory's Very Large Telescope, used data from NASA's HETE-2 satellite to guide the observations, and the fading source was found. "That was the clue we were waiting for," said Garrett Jernigan, a research physicist at the Berkeley Space Sciences Laboratory. "Bursts seem to come mainly in two varieties - the...

The sharp-eyed Jon Lomberg writes with a correction to today's story on Xena and its moon Gabrielle. Specifically, my statement that adaptive optics 'bounces' the light of a laser off the atmosphere to create an artificial star used in refining the telescope's images. Lomberg rightly points out that what the laser actually does is to excite sodium atoms at a specific height. The glow from this excitation is then tracked and used to adjust for atmospheric distortion. The results, as we have seen, are nothing short of spectacular. What's ahead for adaptive optics? "A future improvement of the technique," writes Lomberg, "would use different lasers to excite other elements at other altitudes, thus giving a more detailed profile of distortion in the atmosphere resulting in more precise adjustments."