Big gun: Pistol shines in the infrared.

The Pistol is an apt name for the brilliant star and surrounding nebula shown in this false-color composite taken in the near-infrared with the Hubble Space Telescope. To astronomers, the nebula is shaped like a gun. At least 60 times as massive as the sun and nearly 10 million times as powerful, the Pistol could be the most energetic star in the heavens. At its birth, when it packed as much as 200 times the sun's mass, it may also have been the heaviest.

Located 25,000 light-years from Earth, the star is intrinsically bright, but intervening dust prevents it from being seen in visible light. That explains why the star was not discovered until sensitive infrared detectors became available in the early 1990s. In 1995, Don F. Figer of the University of California, Los Angeles proposed that the star had generated the surrounding nebula during two violent outbursts 4,000 and 6,000 years ago. The Hubble image, released this week, confirms the association. It also provides further evidence that the Pistol is a rare, unstable type of star known as a luminous blue variable--only the seventh such star detected in our galaxy, Figer says.

These objects may represent a brief transitional phase between ordinary massive stars, known as O stars, and Wolf-Rayet stars, which have ejected their outer layers. Figer's team plans to study the composition and velocity of the Pistol's expanding nebula with the Keck II telescope atop Hawaii's Mauna Kea.