Imma Perfetto
Cosmos science journalist
A stunning image captured by the European Southern Observatory’s Very Large Telescope (VLT) is the first visual evidence to confirm a star remnant has undergone a “double detonation”.
Most supernovae are the explosive deaths of massive stars at least 5 times the mass of the Sun – but not Type Ia supernovae, which are the explosive deaths of white dwarf stars.
They occur in binary star systems when a white dwarf, the dense core left by a dead star like the Sun, gets too close to its companion and accumulates material from it.
The leading model for a Type Ia supernova is that the white dwarf’s mass grows too large, reaching the “Chandrasekhar limit” of about 1.4 times the mass of the Sun, causing it to catastrophically explode.
“The explosions of white dwarfs play a crucial role in astronomy,” says Priyam Das, a PhD student at the University of New South Wales Canberra, Australia, who led the study published in Nature Astronomy.
Type Ia supernovae are also known as “standard candles” because their predictable brightness can be used by astronomers to measure how far away they are from Earth.
“Yet, despite their importance, the long-standing puzzle of the exact mechanism triggering their explosion remains unsolved,” says Das.
This is because the Chandrasekhar mass model cannot account for the full range of Type Ia supernova observations. It has been suggested that some could be better explained by a double explosion before the white dwarf ever reaches the Chandrasekhar limit.
ESO/P. Das et al.
A white dwarf that explodes through this alternate mechanism is thought to collect on its surface a stolen layer of helium from its companion – a helium star or helium-rich white dwarf.
When this layer becomes sufficiently unstable it ignites. This drives a shockwave into the white dwarf’s core triggering a second detonation.
The remnants of these double detonation Type Ia supernovae are expected to display a distinctive pattern consisting of 2 concentric shells of the element calcium.
Now, this pattern has been detected for the first time in the supernova remnant SNR 0509-67.5, located 160,000 light-years away in the Large Magellanic Cloud.
Co-author Dr Ivo Seitenzahl, who was at Germany’s Heidelberg Institute for Theoretical Studies when the study was conducted, says these results show “a clear indication that white dwarfs can explode well before they reach the famous Chandrasekhar mass limit, and that the ‘double detonation’ mechanism does indeed occur in nature”.