Chameleon Supernova Hints At A Different Kind Of Stellar Explosion

A three-color X-ray image of galaxy NGC 7331, with blue representing the highest energy x-rays. Supernova SN 2014C is in the square. NASA/CXC/CIERA/R.Margutti et al 

Supernovae come in two main varieties, depending on if they have hydrogen in their light or not. Exploding stars, then, are either one type or the other. Unless, of course, you are Supernova SN 2014C.

SN 2014C, located in spiral galaxy NGC 7331, has been nicknamed the chameleon supernova. It was a nice Type I (no hydrogen), but over the course of a year it became a Type II (hydrogen!). This seemingly miraculous apparition of hydrogen puzzled scientists, but an international team has now found some intriguing clues as to what happened.

According to a paper published in the Astrophysical Journal, the progenitor star spent decades, if not centuries, ejecting hydrogen and other elements into space, making the supernova explosion hydrogen poor. But in just over a year, the exploded material caught up with the hydrogen shell and the supernova appeared to have gone from one type to the other.  

"Expelling this material late in life is likely a way that stars give elements, which they produce during their lifetimes, back to their environment," lead author Raffaella Margutti, assistant professor of physics and astronomy at Northwestern University, said in a statement.

The researchers used NASA’s NuSTAR (Nuclear Spectroscopic Telescope Array) to look at the X-ray emissions of both the exploded material and the ejected shell. The team estimate that the shell was as massive as the Sun, a completely baffling result as heavy stars are not known for such a hefty discharge.

"This 'chameleon supernova' may represent a new mechanism of how massive stars deliver elements created in their cores to the rest of the universe," added Margutti.

The astronomers put forward two different scenarios to explain this unique event. First, the star that became SN 2014C might have had a companion that helped create the unusual circumstances of its death. About 70 percent of massive stars are in binary systems, so this is a compelling solution.

The other possibility is that we don’t have a complete picture of stellar demise. Given that there are only a handful of supernovae per galaxy per century, we might indeed have a small population of peculiar supernovae.

 

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