Scientists have observed an explosion in space that is challenging our current understanding of cosmic explosions. The explosion, which occurred 180 million light-years from Earth, was much flatter than any previously seen in space.
Typically, explosions in space are spherical, as the stars themselves are spherical, but this particular one was the most aspherical ever seen by astronomers. The explosion was an extremely rare Fast Blue Optical Transient (FBOT) and is only the fifth of its kind ever seen.
FBOTs are much less common than other explosions, such as supernovas, and very little is known about them. The first bright FBOT was discovered in 2018 and given the nickname “the cow.” Seems silly, but astronomers gave FBOTs this nickname because of the way it appeared in telescope images.
When it was first discovered in 2018, the explosion looked like a bright, glowing spot surrounded by a cloud of gas and dust. To some astronomers, this cloud looked like the silhouette of a cow, and the name stuck. They behave unlike any other exploding star known to astronomers. And It is still unclear just how bright FBOT explosions are, but scientists hope that this observation will bring us closer to understanding them.
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Scientists made the discovery by spotting a flash of polarised light completely by chance. They were able to measure the polarisation of the blast with the Liverpool Telescope located on La Palma. By measuring the polarisation, 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 2.0m in diameter, but by studying the polarisation, the astronomers were able to reconstruct the shape of the explosion as if the telescope had a diameter of about 750km.
Potential FBOT explanation baffles scientists
So how did this rare explosion occur? Scientists don’t know for sure – but have some interesting theories.
Dr Justyn Maund, the lead study author from the University of Sheffield’s Department of Physics and Astronomy, said that there are a few potential explanations for the asymmetry of the explosion. 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 into a black hole or neutron star which then eats the rest of the star.
“Very little is known about FBOT explosions,” said Dr Maund. “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.”
Dr Maund highlighted that all scientists 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.
The researchers’ next step is 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 observation of this explosion, published in Monthly Notices of the Royal Astronomical Society, is an important step towards unravelling the mysteries of FBOTs.
A small explosion in comparison
Yes – an explosion the size of our solar system sounds massive. In Astronomical Units (1 AU is the distance between the Earth and Sun), the solar system has an approximate estimated diameter of somewhere close to 100 AU. But this pales in comparison to some of the grandest explosions ever observed by astronomers.
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In 2006, scientists at the University of Texas observed the most explosive supernovae to date, dubbed SN 2006gy. Determining the exact size of the explosion is challenging because it happened 238 million light years from Earth. But according to best estimates, the SN 2006gy explosion was likely between 300 and 600 times larger than our Sun, meaning the explosion may have been roughly equivalent to a radius of 500 astronomical units (AU).
In August 2020, NASA’s Fermi Gamma-ray Space Telescope detected a supernova that occurred 6.6 billion years ago. Commonly known as a gamma-ray burst (GRB), this particular explosion was one for the books.
“GRBs are the most powerful events in the universe, detectable across billions of light-years,” NASA reports. “ Astronomers classify them as long or short based on whether the event lasts for more or less than two seconds. They observe long bursts in association with the demise of massive stars, while short bursts have been linked to a different scenario.”
Needless to say, we have spotted some whopping cosmic explosions over the years. Going forward, astronomers hope to study FBOTs in greater detail. But in all honesty – we’re waiting for the day the first “Elon” shaped explosion is detected. That will be one for the books.