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Ghost Of Exploded Star, Now the Crab Nebula, Captured by the HubbleSpace Telescope
By Maia Weinstock
Staff Writer
posted: 07:00 am ET
01 June 2000
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hubble_crabneb_000601 The ghost of a giant stellar explosion that was first witnessed by Chinese astronomers 946 years ago was recently captured in high detail by the Hubble Space Telescope. The image of the stars ghostly remains was created by combining five color-filtered pictures taken with the telescope's Wide Field and Planetary Camera 2 instruments. Though remnants of this ancient explosion currently look much different than they would have at the time of the original bang, scientists say the object, known as the Crab Nebula, is obviously a descendant of a brilliant star described in Chinese accounts. "Some Chinese records are ambiguous, but this one was pretty clearly indicated in a small region of the sky," said William Blair, an astrophysicist at Johns Hopkins University in Maryland. "When we look at that region today, there sits the Crab Nebula. The inference is pretty clear." 
"Nature has been kind in providing such a glorious example of a stellar ghost for us to study."
The star that exploded to form the Crab Nebula was originally about 10 times as massive as our own sun. According to Chinese records, the star exploded on July 4, 1054 and would have been visible as a bright star in the sky. Scientists say that the material that makes up the Crab was once part of the outer layers of the nebulas parent star. "Initially, the material was heated in the explosion, but as the ejecta expanded, they were able to cool and recombine," said Blair. "Today, we see this material expanding away from the site of the explosion at some 3.3 million miles per hour" (5.3 million kilometers per hour). 
The materials in this latest Hubble Space Telescope image are actually gas filaments that glow due to interactions with the remains of its dead stars central core. Today, the core is a pulsar, a failed star that spins on its axis 30 times a second. "The spinning pulsar energizes a diffuse cloud of surrounding low-density gasthats the ghostly diffuse light in the Hubble picture," explained Blair. "The gas in turn emits light that is absorbed by the filaments, heating them and causing them to glow." The next thousand years will bring continued expansion to the glowing filaments in the Crab Nebula, said Blair. Further on down the line, perhaps in 100 thousand years, these materials will slow down and begin to incorporate themselves into new stars, and even planets. This process is thought to be similar to the process by which our own solar system formed. "While we cant watch it happen for our solar system, the next best thing is to observe the process happening elsewhere," said Blair. "Nature has been kind in providing such a glorious example of a stellar ghost for us to study."
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