Can a Dead Star Keep Exploding?

This is an artist’s representation of AT2022tsd, an explosion in a distant galaxy. The image shows one possible explanation for the strange object. It could be a black hole accreting matter from a disk and powering a jet. Variation in the jet's direction could produce the observed rapid flashes. Image Credit: Robert L. Hurt/Caltech/IPAC

In September 2022, an automated sky survey detected what seemed to be a supernova explosion about one billion light-years away. The Zwicky Transient Facility (ZTF) spotted it and gave it the name AT2022tsd. But something was different about this supernova. Supernovae explode and shine brightly for months, while AT2022tsd exploded brightly and then faded within days.

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A Stellar Explosion Mimicked the End of the Death Star

In 1997, George Lucas released the special edition remaster of his Star Wars trilogy, making changes to the special effects that both delighted and divided fans worldwide (did Han shoot first?). Among the myriad additions was a visually spectacular ring-shaped shockwave emanating from the exploding Death Star, and Alderaan too. Star Trek fans will delightedly point out that this particular special effect had previously been used in the 1991 film Star Trek VI: The Undiscovered Country, in which the Klingon moon Praxis explodes, giving the effect its name: the Praxis ring. Hollywood lore suggests Lucas was so impressed with the effect in that film that he added it to Star Wars too.

Praxis rings look cool on the silver screen, but we all know explosions in space are supposed to be spherical. With no preference for up, down, left, or right, the material blown off an exploding star should push outward in all directions.

Except when it doesn’t. A paper published at the end of March described the flattest explosion ever observed, with a disc of material ejecting out from the core along one plane, just like the Praxis effect.

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A New Kind of Supernova Explosion has been Discovered: Fast Blue Optical Transients

Artist's conception illustrates the differences in phenomena resulting from an "ordinary" core-collapse supernova explosion, an explosion creating a gamma-ray burst, and one creating a Fast Blue Optical Transient. Credit: Bill Saxton, NRAO/AUI/NSF

For the child inside all of us space-enthusiasts, there might be nothing better than discovering a new type of explosion. (Except maybe bigger rockets.) And it looks like that’s what’s happened. Three objects discovered separately—one in 2016 and two in 2018—add up to a new type of supernova that astronomers are calling Fast Blue Optical Transients (FBOT).

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