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|This image from NASA’s Chandra X-ray Observatory shows spiral galaxy NGC 7331, center, in a three-color X-ray image. Red, green and blue colors are used for low, medium and high-energy X-rays, respectively. An unusual supernova called SN 2014C has been spotted in this galaxy, indicated by the box.|
“We’re made of star stuff,” astronomer Carl Sagan famously said.
“This ‘chameleon supernova’ may represent a new mechanism of how massive stars deliver elements created in their cores to the rest of the universe,” said Raffaella Margutti, assistant professor of physics and astronomy at Northwestern University in Evanston, Illinois. Margutti led a study about supernova SN 2014C published this week in The Astrophysical Journal.
A supernova mystery
|This visible-light image from the Sloan Digital Sky Survey shows spiral galaxy NGC 7331, center, where astronomers observed the unusual supernova SN 2014C. The inset images are from NASA’s Chandra X-ray Observatory, showing a small region of the galaxy before the supernova explosion (left) and after it (right). Red, green and blue colors are used for low, medium and high-energy X-rays, respectively.|
In the new study, NASA’s NuSTAR (Nuclear Spectroscopic Telescope Array) satellite, with its unique ability to observe radiation in the hard X-ray energy range — the highest-energy X-rays — allowed scientists to watch how the temperature of electrons accelerated by the supernova shock changed over time. They used this measurement to estimate how fast the supernova expanded and how much material is in the external shell.
To create this shell, SN 2014C did something truly mysterious: it threw off a lot of material — mostly hydrogen, but also heavier elements — decades to centuries before exploding. In fact, the star ejected the equivalent of the mass of the sun. Normally, stars do not throw off material so late in their life.
“Expelling this material late in life is likely a way that stars give elements, which they produce during their lifetimes, back to their environment,” said Margutti, a member of Northwestern’s Center for Interdisciplinary Exploration and Research in Astrophysics.
Challenging existing theories:
“The notion that a star could expel such a huge amount of matter in a short interval is completely new,” said Fiona Harrison, NuSTAR principal investigator based at Caltech in Pasadena. “It is challenging our fundamental ideas about how massive stars evolve, and eventually explode, distributing the chemical elements necessary for life.”