Chameleon Supernova: Exploding star undergoes complete Metamorphosis

25 Jan

A team of astronomers led by Raffaella Margutti (Northwestern University) , including Manos Zapartas, PhD student at the University of Amsterdam,  have found a most peculiar supernova explosion, SN2014C, one that defies all established categories of how astronomers thought explosions look like.  It underwent a complete metamorphosis in the year after it died.  Astronomers are calling it the Chameleon Supernova.

When massive stars die they explode during which they create many of the chemical elements that exist in the Universe, including the elements that we ourselves are made of.  Astronomers are trying hard to understand how this works, but the Universe keeps presenting them with new puzzles.

SN 2014C, discovered in 2014 in a spiral galaxy about 40 million light-years away, is unlike any other.  The exploding star did not show any evidence for hydrogen (which astronomers classify as type I).  Astronomers kept studying the location of the explosion and to their surprise the found that the explosion suddenly started show signs of hydrogen (which astronomers classify as type II).  It was clear that shock waves of the explosions were hitting a shell material outside the star. These results were published earlier in a study lead by Dan Milisavljevic at the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA.

The paper that will be published in Astrophysical Journal is presenting new observations of SN2014C taken with NASA’s new satellite NUSTAR, which can observe the highest energy X-rays.  It appears that the star ejected a large amount of material shortly before dying, surrounding the star as a cocoon. The astronomers used this to measure how much material is present in the cocoon of material and how fast it is expanding.

The observations are challenging the existing ideas about how massive stars die. Why would the star throw off so much hydrogen before exploding?  Astronomers at the University of Amsterdam have been investigating this using computer simulations.

One theory is that there is something missing in our understanding of the nuclear reactions that occur in the cores of massive, supernova-prone stars. This could cause them to suddenly eject their outer layers just before they die. The second possibility is that the star formed part of a binary systems and that a companion star helped the star to get rid of its outer layers.  The second theory fits with other observations that show that 7 out of 10 massive stars are found in close binary systems.

Astronomers are now eager to find more supernova that show similar behaviour to give more clues about the physics.  They are scanning the sky every night to try and catch the light of more stars that explode.

  • Preprint Main Paper by R. Margutti, A. Kamble, D. Milisavljevic, E. Zapartas & S.E. de Mink et al. (2017), accepted for publication in the Astrophysical journal.  Preprint
  • Preprint related theory paper Zapartas, de Mink, Izzard, Yoon & Badenes et al. (2017) accepted for publication in Astronomy & Astrophysics. Preprint: Zapartas_deMink_Izzard_AA_2017
  • Link to NASA’s press release