The newly-observed stellar explosion, named AT2018cow, occurred approximately 180 million light-years away from Earth and belongs to a special class called Fast Blue Optical Transients (FBOTs).
An artist’s impression of the AT2018cow stellar explosion. Image credit: Phil Drury, University of Sheffield.
Stellar explosions in the Universe are almost always spherical in shape, as the stars themselves are spherical.
However, AT2018cow is the most aspherical ever seen in space, with a shape like a disk emerging a few days after it was discovered.
This section of the explosion may have come from material shed by the star just before it exploded.
“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,” said Dr. Justyn Maund, an astronomer at the University of Sheffield.
“Put simply, they are weird, and this new observation makes them even weirder.”
“Hopefully this new finding will help us shed a bit more light on them — we never thought that explosions could be this aspherical.”
“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 supernovae, where the core of the star collapses to a black hole or neutron star which then eats the rest of the star.”
“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.”
Dr. Maund and colleagues discovered AT2018cow using the Liverpool Telescope on the Spanish island of La Palma, off the coast of north-west Africa.
By measuring the polarization of the blast, it allowed them to measure the shape of the explosion, effectively seeing something the size of our Solar System but in a galaxy 180 million light-years away.
They were then able to use the data to reconstruct the 3D shape of the explosion, and were able to map the edges of the blast — allowing them to see just how flat it was.
The mirror of the Liverpool Telescope is only 2 m in diameter, but by studying the polarization the astronomers were able to reconstruct the shape of the explosion as if the telescope had a diameter of about 750 km.
“We plan to undertake a new survey with the international Vera Rubin Observatory in Chile, which is expected to help discover more FBOTs and further understand them,” the researchers said.
Their paper appears in the Monthly Notices of the Royal Astronomical Society.
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Justyn R. Maund et al. 2023. A flash of polarized optical light points to an aspherical ‘cow.’ MNRAS 521 (3): 3323-3332; doi: 10.1093/mnras/stad539
