For the first time, a team of astronomers has captured a clear image of a white dwarf star that exploded not just once, but twice, as a Type Ia supernova — a «double-detonation» that scientists hadn’t thought possible until now. The extraordinary observation could revise our long-held notions of how stars die, suggesting that some stars can explode as supernovas without ever crossing the Chandrasekhar limit, the minimum mass normally thought necessary for such an explosion. The astronomers employed the Very Large Telescope’s MUSE instrument to zoom in on the four-century-old supernova remnant SNR 0509-67.5, which sits 60,000 light-years away in the constellation Dorado, revealing evidence of two separate blasting catastrophes in its construction.
First Visual Proof Shows White Dwarfs Can Explode Twice Without Reaching Chandrasekhar Limit
As the researchers report on July 2 in Nature Astronomy, the team found a distinctive “fingerprint” in the debris of SNR 0509-67.5 in the Large Magellanic Cloud that the models predicted. White dwarfs—which are the dead stage of sun-like stars—usually blow up into Type Ia supernovas after they hit the Chandrasekhar limit by stealing matter from a neighbouring star.
However, this finding shows that the detonation can be launched at an earlier time. The explosion is likely to have a two-step origin, the team argues, with the initial blast being generated when an unstable layer of helium that the star had acquired exploded on its surface; the resulting shock wave then drove a second and main detonation.
“This physical proof of a double-detonation not only helps solve a long-standing mystery of what causes these explosions, but it represents the most visually compelling evidence for this origin.” Priyam Das, University of New South Wales, team leader and author.
Something is happening to Type Ia supernovas, the “standard candles” used to measure cosmic distances, because their brightness doesn’t fluctuate. But they have long mystified scientists with how they explode. Until this discovery, an explosion white dwarf that didn’t surpass the Chandrasekhar limit was only considered in theory.
This fresh visual evidence for the double detonation model further informs our knowledge of stellar evolution and also informs how we should interpret light from distant supernovas. More than its scientific implications, its discovery adds a colourful new page to the story of dying stars — stars that, as it now appears, will not go gently into that night but will light up the sky twice over in fantastic fireworks before vanishing from the cosmos.
