Back in 2018, astronomers discovered a very peculiar stellar explosion, which got the automatic name of AT2018cow. Since then, it's become known simply as the “cow” and it is the prototype of a new class of objects called Fast Blue Optical Transients (FBOTs). And researchers have now realized that the event was even weirder than previously assumed.
This explosion appeared to be extremely flat, spreading through a thick disk, with a thickness about one-tenth of the radius of the disk a handful of days after the explosion was recorded. Explosions in space can have a level of asymmetry, but this is the most aspherical ever recorded, which could be an indication of the properties of all FBOTs.
“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. Put simply, they are weird, and this new observation makes them even weirder,” lead author Dr Justyn Maund, from the University of Sheffield, said in a statement.
“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 continued.
The crucial element in this work was the polarization of light. Light is made by oscillating electric and magnetic fields, and these oscillations can point in any direction. If the light is polarized, it means the oscillation is happening in a specific direction. This approach is what is used in 3D cinema. Light with two polarizations is sent out and each lens filters part of it out, giving the impression to our brains that we are seeing something in 3D.
A flash of polarized light was measured from this event and it allowed the team to measure the shape of the explosion. It revealed that the flat disk was roughly the size of the Solar System at that point.
“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 supernovas, where the core of the star collapses to a black hole or neutron star which then eats the rest of the star,” Dr Maund explained.
There are only four other known FBOTs, so humanity’s understanding of them remains limited. Upcoming facilities like the Vera Rubin Observatory are expected to find even more of these events, and maybe find out if this extremely flat explosion is an outlier or not.
The study is published in the Monthly Notices of the Royal Astronomical Society.