Mysterious flares of light in deep space may be driven by stellar corpses, new study suggests

(CN) — In a study published in Nature on Wednesday, dozens of scientists from around the world propose a ghostly explanation for mysterious blue-tinted light bursts in deep space.

The little-understood phenomena known as fast blue optical transients, or luminous fast blue optical transients — FBOTS or LFBOTS — superficially resemble supernovae.

But the new study argues they aren't driven by the violent death of massive stars — at least, not directly.

Instead, the authors of the paper suggest they are created by the activity of dead stars already in their afterlife, specifically "compact objects" like a neutron star or stellar mass black hole.

The researchers used 15 telescopes to analyze intermittent flares of light as bright as a supernova emanating from an LFBOT about a billion light years from Earth, officially labeled AT2022tsd but colloquially dubbed the Tasmanian Devil.

The flares from the Tasmanian Devil each lasted mere minutes, but they began occurring weeks after Cornell University professor Anna Ho, lead author of the paper, discovered the LFBOT's initial explosion in September 2022. They then continued for more than three months after. The flares were as bright as the initial explosion and emitted energetic bursts of X-rays, radio waves and red visible light.

"Supernovae, they happen once and then they're done. This LFBOT, it's ejecting material over the course of 100 days," Ho said.

When other astronomers discovered the first-known LFBOT, called The Cow, in June 2018, they quickly noted its differences from a garden-variety supernova. The Cow lacked the Tasmanian Devil's flares — though Wednesday's paper suggested it may simply have been at the wrong angle relative to Earth for researchers to see them — but it displayed traits common to all subsequently discovered LFBOTs.

It was tinted blue. It shone many times brighter than a typical supernova, but faded in only a matter of days rather than over the course of weeks. And its X-ray emissions were strangely chaotic, becoming brighter even as the visible light of the explosion dimmed.

Exactly what LFBOTs are, and what creates them, is still an open question. But the Tasmanian Devil's flares are the first phenomenon of their type ever observed, and Ho said they may have helped her and her colleagues get closer to an answer.

"We conclude that the flares in [the Tasmanian Devil] arose from a near-relativistic outflow that was powered by a compact object over a period of 100 days," the study's authors wrote. "For the compact object, a supermassive black hole is highly unlikely given the location of [the Tasmanian Devil] ... from the nucleus of a star-forming galaxy and the rapid timescale of the initial LFBOT. The possible power sources for the outflow are therefore the rotational spindown of a newborn neutron star or accretion onto a stellar-mass or intermediate-mass compact object."

In layman's terms, this means that some massive but relatively small and extremely dense object may be vacuuming up gas and dust — possibly from a nearby star whose outer layers it's consuming — into an accretion disc, and then shooting the luminous material back out into space at more than half the speed of light.

Ho added that unlike the rhythmic emissions of pulsars, another type of stellar remnant that emits electromagnetic energy at regular intervals, there didn't seem to be any pattern to the Tasmanian Devil's flares.

"We thought about pulsars," Ho said. "But there's no real periodicity that we've seen."

One phenomenon the flares did resemble, Ho noted, is another class of energetic event known as a gamma ray burst. As their name suggests, gamma ray bursts emit massive amounts of gamma rays and are typically thought to be driven by black holes.

Ho said the resemblance between the Devil's flares and gamma ray bursts may suggest the phenomena are related, with both processes driven by a black hole ejecting accreted matter away from itself. The differences between the two may just be an issue of how large the black hole's reservoir of material is - More material might be blown away in the initial explosion of a gamma ray burst, while LFBOTs have more residual stellar matter to draw from.

But there are still many mysteries surrounding LFBOTs, and Ho stressed that the new paper was merely putting forth one set of ideas. As scientists continue to study the Tasmanian Devil and other LFBOTs, different explanations as to what causes them may emerge.

"We don't know what they are. That's what we're really trying to study," Ho said.

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