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Violent Helium Reaction on White Dwarf Surface Triggers Supernova Explosion

posted by Fnord666 on Sunday October 08 2017, @07:58AM   Printer-friendly
from the high,-squeaky-voice dept.

"exec" writes:

Arthur T Knackerbracket has found the following story:

An international team of researchers has found evidence a supernova explosion that was first triggered by a helium detonation, reports a new study in Nature this week.

A Type Ia supernova is a type of white dwarf star explosion that occurs in a binary star system where two stars are circling one another. Because these supernovae shine 5 billion times brighter than the Sun they are used in astronomy as a reference point when calculating distances of objects in space. However, no one has been able to find solid evidence of what triggers these explosions. Moreover, these explosions only occur once every 100 years in any given galaxy, making them difficult to spot.

"Studying Type Ia supernovae is important because they are a valuable tool researchers use to measure the expansion of the universe. A more precise understanding of their history and behavior will help all researchers obtain more accurate results," said author and University of Tokyo School of science Professor Mamoru Doi.

-- submitted from IRC

Ji-an Jiang, et. al. A hybrid type Ia supernova with an early flash triggered by helium-shell detonation. Nature, 2017; 550 (7674): 80 DOI: 10.1038/nature23908

Original Submission

 
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  • (Score: 3, Informative) by stormwyrm on Sunday October 08 2017, @09:40PM (4 children)

    by stormwyrm (717) on Sunday October 08 2017, @09:40PM (#578992) Journal
    A white dwarf can also go supernova. [wikipedia.org] A white dwarf in a binary system slowly gains mass by accretion from its companion, sometimes going nova as matter caught in its gravity gets hot enough to ignite nuclear fusion. At some point though the dwarf gets so much mass until eventually it becomes dense enough to ignite carbon fusion. Since the matter of the dwarf is degenerate, it cannot expand to cool the way a normal star would, so the entire dwarf blows itself apart in a runaway fusion reaction easily the equal of any giant star collapsing under its own gravity. This generally doesn't leave any remnant behind. This happens when a dwarf reaches a certain mass limit so these kinds of supernovae are thought to be of more or less equal luminosity no matter where they occur in the universe, and as such they are used as standard candles. Their spectra are also rather distinctive since they are just about completely carbon and oxygen fusion, making them look quite different from a massive star supernova and easy to identify.
    --
    Numquam ponenda est pluralitas sine necessitate.
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  • (Score: 0) by Anonymous Coward on Sunday October 08 2017, @11:07PM (3 children)

    by Anonymous Coward on Sunday October 08 2017, @11:07PM (#579020)

    Ah. So, they are different things.

    Going back to TFA, there's

    The extra helium coating [???] the star would trigger a violent burning reaction, which in turn would trigger the star to explode from within as a supernova

    -- OriginalOwner_ [soylentnews.org]

    • (Score: 2) by stormwyrm on Monday October 09 2017, @02:38AM (2 children)

      by stormwyrm (717) on Monday October 09 2017, @02:38AM (#579078) Journal
      The paper seems to be an elucidation of the precise mechanism involved in the triggering of a type Ia supernova, which is still something of a mystery. The way I understand it, a white dwarf that is already almost massive enough to detonate in the way described might near the end accumulate a mantle of helium from its companion star, which experiences nuclear fusion from the dwarf's gravity and thereby compresses the rest of the dwarf past the critical point, sort of the way primary fission devices compress into nuclear fusion the secondary of a thermonuclear bomb (my own analogy, possibly wrong). I can't read the actual paper as it's behind a paywall, but that's the way I understand it based on the abstract. The result is useful in that it could allow astronomers to better estimate the actual luminosity of such supernovae, thereby making their estimates of distances across the universe better.
      --
      Numquam ponenda est pluralitas sine necessitate.

      • (Score: 2) by maxwell demon on Monday October 09 2017, @08:36AM (1 child)

        by maxwell demon (1608) on Monday October 09 2017, @08:36AM (#579190) Journal

        I can't read the actual paper as it's behind a paywall

        https://arxiv.org/abs/1710.01824 [arxiv.org]

        --
        The Tao of math: The numbers you can count are not the real numbers.

        • (Score: 2) by stormwyrm on Tuesday October 10 2017, @01:40PM

          by stormwyrm (717) on Tuesday October 10 2017, @01:40PM (#579770) Journal

          Thank you. What I can understand of the paper seems to indicate that my analogy of nuclear bomb primaries and secondaries was not an unreasonable one. From page 6: "In principle, a He-shell detonation not only generates a shock wave propagating toward the center of the white dwarf (WD) and ignites carbon burning near the center..." Thermonuclear bomb fission primaries produce shock waves that are supposed to compress and heat the secondary enough to ignite fusion, and in a similar way, a shell of helium undergoing fusion around a white dwarf can produce shock waves that would ignite carbon fusion in the centre.

          --
          Numquam ponenda est pluralitas sine necessitate.