The dimmest ever exploding star has been spotted by the twin ATLAS telescopes in Hawaii. Solving the mystery of how the explosion happened could have implications for how we measure the expansion rate of the universe.
One theory for the origin of this peculiar astronomical event – 150 million light years away – is that it is a failed or incomplete detonation of a small, very dense star called a white dwarf. Stars of low to medium mass like the sun become white dwarfs after they have burned all their fuel.
Explosions of white dwarfs, called type Ia supernovae, are usually very bright. Cosmologists rely on their characteristic and consistent brightness as benchmarks, or “standard candles”, to measure how quickly our universe is expanding.
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Dimmer type Ia supernovae, dubbed type Iax, were known to exist, but over the past 12 years, three exceptionally dim events have been picked up by telescopes – including this very recent one, which is the faintest so far and about 100 times dimmer than a typical type Ia supernova.
Failed explosions
“I’m excited to see if we can confirm the idea that these are failed explosions of white dwarfs,” says Shubham Srivastav at Queen’s University Belfast in the UK, who led the discovery.
“This could potentially be the product of a low-mass white dwarf that started burning and ran out of fuel,” says Boris Gänsicke at the University of Warwick in the UK, who wasn’t involved in the work.
Srivastav and his team identified a mixture of elements – carbon, oxygen, magnesium, silicon and sulphur – which are intermediate products formed during white dwarf explosions, hinting at an incomplete event.
If confirmed, Srivastav says these unusually dim supernovae might need to be excluded from the “standard candles” – astronomical objects used for calculating the expansion rate of the universe. “Understanding these events in more detail would help to filter the samples that are used for cosmology,” says Srivastav.
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