Stars are basically spherical, and when they explode, the explosions are spherical too. Most of the time.
But an international team of astronomers has observed a disc-shaped explosion – the thinnest yet known to science.
The explosion is called a Fast Blue Optical Transient (FBOT): a rare event that astronomers have only known about for the past five years. They’re also called ‘cows’.
“Very little is known about FBOT explosions – they just don’t behave like exploding stars should, they are too bright and they evolve too quickly,” says Dr Justyn Maund, a researcher in the Department of Physics and Astronomy at the University of Sheffield, UK, and lead author on a study describing the FBOT, published in Monthly Notices of the Royal Astronomical Society.
“Put simply, they are weird, and this new observation makes them even weirder.”
The FBOT they’ve observed is 180 million light-years away, and about the size of the Solar System. They spotted it by chance, using observations from the Liverpool Telescope in the Canary Islands.
“Hopefully this new finding will help us shed a bit more light on them – we never thought that explosions could be this aspherical,” says Maund.
“There are a few potential explanations for it: the stars involved may have created a disc just before they died or these could be failed supernovas, where the core of the star collapses to a black hole or neutron star which then eats the rest of the star.”
The researchers figured out the size and shape of the explosion by examining polarised light – like a pair of telescopic sunglasses – from the telescope.
“What we now know for sure is that the levels of asymmetry recorded are a key part of understanding these mysterious explosions, and it challenges our preconceptions of how stars might explode in the universe,” says Maund.
They’re planning to follow these observations up, and look for more FBOTs, with the Vera Rubin Observatory in Chile.