‘White dwarf’ triggers giant supernovae explosion

Some of the brightest known explosions in the universe, type 1a supernovae, are triggered by ancient, dense stars called white dwarfs.

London: Some of the brightest known explosions in the universe, type 1a supernovae, are triggered by ancient, dense stars called white dwarfs, a new study has revealed.

These supernovae are such regular features of the Universe that astrophysicists use them to measure cosmic distances. But still the causes behind these giant explosions are still unknown.

Now, scientists at the Weizmann Institute of Science, as part of an international effort to study supernovae, are beginning to clear up the mystery of why certain stars explode in a brilliant display at the ends of their lives.

New research began last August, when the automatic telescopes at the Palomar Transient Factory (PTF) in California that search for signs of developing supernova spotted one just a half a day into the explosion process.

Not only was this a very early observation, but also the supernova was in the Pinwheel Galaxy a mere 6.4 Megaparsecs away – the closest one in the last 25 years.

Data on the new supernova came from X-ray and radio wave telescopes, both Earth- and satellite-based.

In addition, the researchers, including Dr. Eran Ofek and Dr Avishay Gal-Yam of the Particle Physics and Astrophysics Department, went over images of the Pinwheel Galaxy taken by the Hubble Space Telescope over the years to see if they could detect pre-explosion signs of the system that gave rise to the supernova.

The team’s results, including an analysis of the material thrown off in the blast and of the “shock breakout” that takes place as the light released in the shockwave passes through the mass of erupting material, showed that the exploding star was, as predicted, a white dwarf: an extremely compact star with a diameter much smaller than that of our sun.

And while the team did not manage to discount either category, they set an upper limit on the size of a possible companion, showing it could not have been a particularly large star, such as a red giant.

“Although we can’t rule out a white dwarf merger,” said Ofek

“Our results point to another likely scenario in which a medium range star – close to our sun’s size – supplied the white dwarf with the extra material needed to turn it into a supernova,” Ofek added.

The study has been recently published in three new papers, two of them appearing in Nature and one in The Astrophysical Journal.


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