The Crab nebula is the result of a type II supernova explosion observed by Chinese astronomers in 1054. The nebula consists of the outer parts of a red supergiant that exploded after having burned all its fuel.
Credit: Hubble Space Telescope
Telescope images have confirmed something astronomers have long suspected, that red supergiant stars are the stars that explode in so-called type II supernovas.
Type II supernovas are the impressive cosmic explosions that result from the internal collapse of a massive star. (For this reason, they are also known as core-collapse supernovas.)
On average, a supernova will occur about once every 50 years in a galaxy the size of the Milky Way. But scientists don't know when these stellar powder kegs will blow, so identifying the star that birthed them, called the progenitor star, can be tricky.
Models and observations had suggested that red supergiants were the progenitors of type II supernovas, but the best evidence so far has only been able to show that these stars were in the area before the supernova, not that that they were in the exact spot.
So astronomer Justyn Maund of the University of Copenhagen in Denmark and the University of California, Santa Cruz, and his colleagues used telescope images to answer the question, "How sure are we that this is the progenitor?" he said.
They used images from the Hubble Space Telescope and Gemini Telescope from before and after two supernova explosions, SN 2003gd and SN 1993J. They found that there were indeed red supergiants in the exact spots where the blasts occurred beforehand, and that after, "the progenitor is missing," Maund said.
The finding, detailed in the March 20 issue of the journal Science, confirms the long-standing theory behind type II supernova formation. "There's no other way you could get around it in this case," Maund told SPACE.com.
It takes awhile for scientists to get such confirmations because they have to wait for the glare of supernovas to die down before they can get a proper "after image," which can take many years.
Maund and his team were able to estimate that the progenitor stars had masses that were about seven times the mass of our sun. They were also able to show that SN 1993J's companion, which sucked away much of its partner's outer hydrogen envelope, was still hanging around.
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