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Title: New Evidence That Some Supernovae May Be a 'Double Detonation'

Link: https://science.slashdot.org/story/25/07/03/0...

New evidence from a 300-year-old supernova remnant in the Large Magellanic
Cloud suggests that some Type Ia supernovae may result from a "double
detonation" -- where a helium shell ignites first, triggering a second core
explosion in a white dwarf before it reaches critical mass. "While the
physics of the process itself are interesting, the key question this raises
is whether type Ia supernovae really are all equally bright," writes Ars
Technica's John Timmer. "If they can detonate with substantially less mass
than is needed for direct ignition of the core, then it's possible that some
of them could be considerably less bright." However, the research team notes
that additional factors -- such as the influence of binary systems or
secondary detonations -- could further complicate the picture. Ars Technica
reports: "The detonations in the carbon-oxygen core and the helium-rich shell
result in qualitatively different yield products," the researchers behind the
new work write in a paper describing it. In the paper, they focus on calcium,
which there are two ways of producing. One is from the outer shell of helium,
via fusion before the detonation dilutes the material. A second batch of
calcium is produced through the fusion of the core material as it's ejected
in the supernova, which prevents further fusion events from converting it to
even heavier elements. (Material deeper in the core does end up getting fused
into heavier material.) Because it's produced by both of the detonations,
models predict that the expanding sphere of debris will contain two different
shells of calcium, with some space in between them. To find evidence for
these shells, the researchers checked an older supernova remnant, which
allows enough time for the movement of material to separate the shells by
enough distance that they can be resolved from Earth. They focused their
observations on a supernova remnant named SNR 0509-67.5, located in the
nearby Large Magellanic Cloud. SNR 0509-67.5 is estimated to be a bit over
300 years old, meaning material has had enough time to move a significant
distance away from the site of the explosion. Imaging using a spectrograph on
the Very Large Telescope allowed them to resolve what, in effect, was a
spherical sulfur sandwich, with the role of the bread played by calcium. In
other words, if you were to travel away from the site of the explosion, you
would first hit a layer of ionized calcium, followed by ionized sulfur, and
then run into a second layer of ionized calcium. This is exactly what
computer models that simulate double detonations predict. So, the researchers
suggest it is strong support for that hypothesis. The researchers say that
the details suggest that SNR 0509-67.5 was a white dwarf with roughly the
same mass as the Sun when it exploded, and that its explosion was likely
triggered by the detonation of a helium shell with only three percent of the
Sun's mass.

Read more of this story at Slashdot.

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