AMNH: The Prolonged Death of Light from Type Ia Supernovae

[bystander]

The Prolonged Death of Light from Type Ia Supernovae
American Museum of Natural History | 2016 Feb 25

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Three years after its explosion, a type Ia supernova continues to shine brighter than expected, new research finds. The observations, made with the Hubble Space Telescope and published today in The Astrophysical Journal, suggest that the powerful explosions produce an abundance of a heavy form of cobalt that gives the heat from nuclear decay an extra energy boost. The work could help researchers pinpoint the parents of type Ia supernovae—a type of stellar explosion that is frequently used to measure distances to faraway galaxies—and reveal the mechanics behind these explosions. ...

Current research indicates that type Ia supernova explosions originate from binary star systems—two stars orbiting one another—in which at least one star is a white dwarf, the dense remains of a star that was a few times more massive than our Sun. The explosion is the result of a thermonuclear chain reaction, which produces a large amount of heavy elements. The light that researchers see when a type Ia supernova explodes comes from the radioactive decay of an isotope of nickel (⁵⁶Ni) into an isotope of cobalt (⁵⁶Co) and then into a stable isotope of iron (⁵⁶Fe). Although peak brightness is reached relatively quickly, and most researchers stop watching supernovae after about 100 days past the beginning of the explosion, the light continues to radiate for years.

Previous studies predicted that about 500 days after an explosion, researchers should see a sharp drop-off in the brightness of these supernovae, an idea called the “infrared catastrophe.” However, no such drop-offs have been observed, so Ivo Seitenzahl, a researcher at the Australian National University and the ARC Centre of Excellence for All-sky Astrophysics and one of the co-authors on the paper, predicted in 2009 that it must be due to the radioactive decay of ⁵⁷Co. This is a heavier isotope of cobalt with a longer half-life than ⁵⁶Co, and it is expected to provide an extra energy source that would kick in around two to three years after the explosion. ...

Late-Time Photometry of Type Ia Supernova SN 2012cg Reveals the Radioactive Decay of ⁵⁷Co - Or Graur et al

• Astrophysical Journal 819(1):31 (2016 Mar 01) DOI: 10.3847/0004-637X/819/1/31
  arXiv.org > astro-ph > arXiv:1505.00777 > 04 May 2015 (v1), 25 Feb 2016 (v3)

[bystander]

Supernova Reserve Fuel Tank Clue to Big Parents
Australian National University | 2016 May 19

[img3="Illustration Credit: David A. Hardy / PPARC"]http://www.anu.edu.au/files/styles/anu_ ... 0PPARC.jpg[/img3][hr][/hr]

Some supernovae have a reserve tank of radioactive fuel that cuts in and powers their explosions for three times longer than astronomers had previously thought.

A team of astronomers jointly led by Dr Ivo Seitenzahl from ANU Research School of Astronomy and Astrophysics detected the faint afterglow of a supernova, and found it was powered by radioactive cobalt-57.

The discovery gives important new clues about the causes of Type Ia supernovae, which astronomers use to measure vast distances across the Universe.

Dr Seitenzahl said the discovery of cobalt-57 fingerprints in a Type Ia supernova gave insights into the star that exploded and suggested it was at the top of its weight range.

"This explosion suggested that it was a star stealing matter from an orbiting partner until it got so massive that its core of carbon ignited and set off the explosion," said Dr Seitenzahl. ...

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