remnant, located in the southern constellation Vela. A supernova is the explosive end to the life of a massive star. At the nebulas core is a dying, rapidly spinning neutron star called a pulsar."The 'bang' was probably some 11,000 years ago," said William Blair, a Johns Hopkins University researcher who led the observation. "The expanding blast wave from the explosion is still sweeping outward from the site of the explosion."
The colorful structures are places where the blast wave has run into something, typically a clump or a cloud of interstellar material that is normally invisible, Blair explained in an e-mail interview. The blast heats the material, which then cools down to produce the various colors.
Bluish regions represent hotter gas, struck most recently by the blast, he said. Reddish areas have had time to cool.
"In many other supernova remnants, this seems to happen over very small spatial scales and is difficult to observe," Blair said. "In the Pencil Nebula, the structure is easily resolved, and shows up on both large and small scales."
Also visible in the new picture is a bright star. It is not associated with the nebula, Blair said, but he has not yet calculated its distance. He suspects it is in the background and just happens to be intrinsically very bright.
Hubble's Advanced Camera for Surveys collected the data in October 2002 and the photo was released today. The picture covers an area about three-fourths of a light-year across. The whole Vela supernova remnant is some 114 light-years wide. It all sits about 815 light-years from Earth, which means we see it as it existed 815 years ago.
Unlike other nebulae that reflect light, this one glows because the hot gas emits light.
Other nebulae are often roundish or spherical -- nothing like a pencil. Rounder nebulae are usually smaller, so that the entire thing fits into a camera's field of view, Blair explained. They're also typically created by stars that puff off their outer layers, rather than exploding.
If the age of the Vela supernova is correct, then material must have initially raced out from the star at nearly 22 million miles per hour (35 million kilometers per hour). Since then, everything has slowed down. The portions that make up the Pencil Nebula are moving at roughly 400,000 miles per hour (644,000 kilometers per hour).
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