August 29, 2006—Goodness gracious, this great ball of fire—and by "fire," we mean vast wisps of interstellar gases—is the youngest known remnant of a star explosion in the Milky Way, our home galaxy.

Captured in 2004 and released today, this Hubble Space Telescope image shows a spectacular flameout called Cassiopeia A, located some 10,000 light-years from Earth.

It's all that's left of a star that went supernova 340 years ago, collapsing from the weight of its own gravity, then bursting in a sometimes galaxy-obscuring flash. This was followed by the expansion of its remnant materials—shown here in green (oxygen), red and purple (sulfur), and blue (hydrogen and nitrogen).

Centuries after the Cas A explosion, its gases are still on the move. Comparisons of Hubble images taken at different times reveal that some of the debris is traveling up to 31 million miles an hour (50 million kilometers an hour)—fast enough to go from Earth to the moon in 30 seconds.

—Ted Chamberlain

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