A non-spherical “cow” – a strange explosion the size of our solar system baffles astronomers

Slim Boom. Credit: Phil Drury, University of Sheffield

Astronomers have observed an explosion 180 million light-years away that defies our current understanding of cosmic explosions, and exhibits a much flatter appearance than previously thought.

• Astronomers observed an explosion 180 million light-years away, challenging our current understanding of explosions in space, which appeared much flatter than once thought possible.
• Explosions are always expected to be spherical, as stars themselves are spherical, but this is the flattest of all
• The explosion observed was an extremely rare fast blue burst of light (FBOT) – colloquially known among astronomers as a “cow” – only four others have ever been seen, and scientists don’t know how they happened, but this discovery helped solve part of the puzzle.
• A possible explanation for how this explosion occurred is that the star itself may have been surrounded by a dense disk or it may have been a failed supernova

An explosion the size of our solar system has scientists baffled, as part of its shape – similar to a very flat disk – challenges everything we know about explosions in space.

The observed explosion was a fast blue bright burst of light (FBOT) – an extremely rare class of explosion that is much less common than other explosions, such as supernovae. The first bright FBOT was discovered in 2018 and dubbed the Cow.

Starbursts in the universe are almost always spherical in shape, as the stars themselves are spherical. However, this explosion, which occurred 180 million light-years away, is the most spherical ever seen in space, with a disc-like shape emerging just days after its discovery. This part of the explosion may have been caused by material being thrown out by the star just before it exploded.

It’s still not clear how bright FBOT blasts happen, but it’s hoped that this observation, recently published in the journal Monthly Notices of the Royal Astronomical SocietyIt will bring us closer to understanding it.

Dr Justin Maund, lead author of the study from the University of Sheffield’s Department of Physics and Astronomy, said: “Very little is known about FBOT bursts – they don’t behave like supernovae, they’re very bright and they evolve very quickly. Simply put, they’re weird, and this new observation makes them even more so.” strangeness.

“We hope that this new discovery will help us shed more light on them – we never thought explosions could be non-spherical. There are a few possible explanations for this: perhaps the stars in question created a disk just before their death or these could be failed supernovae, where The star’s core collapses into a black hole or neutron star, which then devours 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 outbursts, and challenge our preconceived notions of how stars explode in the universe.”

Scientists made the discovery after spotting a completely polarized light flash by accident. They were able to measure the explosion’s polarization – using Polaroid-equivalent astronomical eyeglasses – with the Liverpool Telescope (owned by Liverpool John Moores University) located in La Palma.

By measuring the polarimetry, 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. Then they were able to use the data to reconstruct the 3D shape of the explosion, and were able to map the edges of the explosion – allowing them to see how flat it was.

The diameter of the Liverpool Telescope’s mirror is only 2.0 meters, but by studying the polarization, astronomers have been able to reconstruct the shape of the explosion as if it were a telescope with a diameter of about 750 kilometers.

The researchers will now conduct a new survey with the Vera Rubin International Observatory in Chile, which is expected to help discover more FBOTs and further understand them.

Reference: “Polarized optical light flicker refers to an almost spherical ‘cow’” by Justin R. Mond, Peter A. Hoeflich, Ian A. Steele, Wei Yang, Klas Wiersima, Shiho Kobayashi, Nuria Jordana-Metjans, Carol Mondale, Andrea Gombuck, Cristiano Gidorzi and Robert J. Smith, Feb. 21, 2023, Available here. Monthly Notices of the Royal Astronomical Society.
DOI: 10.1093/mnras/stad539