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Hubble camera captures hottest star ever.

For years, astronomers have searched for the hot star that they knew must lie at the center of a Milky Way cloud of dust and gas called NGC 2440. This cloud, or nebula, fluoresces as a result of energetic, ionizing radiation that could only come from a high-temperature star embedded within it. But Earth's turbulent atmosphere acts to smear light from the star with that of the surrounding nebula, preventing ground-based telescopes from viewing the star.

Orbiting above Earth's blurring atmosphere, the Hubble Space Telescope has now captured the first image of that star. Moreover, calculations indicate it has the hottest temperature of any star ever recorded by any telescope, says Sally R. Heap of NASA's Goddard Space Flight Center in Greenbelt, Md.

Sporting a temperature of 200,000 kelvins, the star belongs to a group of hot, dense objects known as white dwarfs, says Heap. White dwarfs represent the final evolutionary stage -- just before complete burnout -- of stars born with a mass no more than a few times that of the sun. Since these dwarfs last for a mere 10,000 years, imaging this star seems a particular feat. "It's as if we've captured this object during its 15 minutes of glory," says Heap, who announced the findings this week at a press conference in Washington, D.C.

She and her colleagues estimated the dwarf's torrid temperature by measuring the surrounding nebula's luminosity -- which comes from ultraviolet radiation emitted by the star -- as well as the visible-light brightness of the star itself.

The nebula formed millions of years ago during a time when the hot star was larger and had more mass. At that epoch, says Heap, the star had evolved into a puffed-up object called a red giant, which eventually blew off its outer envelope of gas and dust, creating the nebula.
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Title Annotation:NGC 2440
Author:Cowen, Ron
Publication:Science News
Date:Apr 25, 1992
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