A rare supernova is helping scientists unlock the mysteries of how these bright, exploding stars come to be.

Animation of a Type1a supernova. Credit: NASA/JPL-Caltech

Why it matters: Supernovas — the violent explosions of some dead stars at the end of their lives — are thought to be responsible for seeding our universe with many of the heavy elements we see around us today. If researchers can figure out exactly how these stellar explosions are created, it could help explain some of the inner-workings of our universe.

Background: On its surface, the supernova in question — named ASASSN-18tb — looked like other Type Ia supernovas, which are typically used to measure distances in our galaxy thanks to their predictable brightness.

  • These types of supernovas are thought to come from the explosions of white dwarf stars — the dead remnants of a sun-like star — in a binary system with another star.
  • Some astronomers think these types of explosions are triggered when a white dwarf eats up a large amount of the material from its companion in the binary, but another hypothesis suggests the explosion occurs when 2 white dwarfs slam into each other.

The big question: The chemistry of ASASSN-18tb is unlike others spotted before.

  • Most Ia supernovas have no hydrogen signature at all, but ASASSN-18tb appears to have ejected some hydrogen when it exploded, causing scientists to question exactly what made the star explode.
  • While some other Type Ia supernovas have been found enveloped in a large amount of hydrogen, ASASSN-18tb didn’t fit the usual model for those kinds of stellar explosions, since those supernovas usually occur in young galaxies that are still forming stars.
  • In contrast, ASASSN-18tb was found in a galaxy with older stars.

What they found: Scientists now think it’s possible the hydrogen ejected by ASASSN-18tb was actually from the white dwarf’s other star in the binary system.

  • “One exciting possibility is that we are seeing material being stripped from the exploding white dwarf’s companion star as the supernova collides with it,” Anthony Piro, one of the authors of the new supernova study in the journal Monthly Notices of the Royal Astronomical Society, said in a statement.
  • “If this is the case, it would be the first-ever observation of such an occurrence.”

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