The cosmos has sent us a series of blue flashes for more than a decade. We now have a clue as to what they really are.

For more than a decade, the cosmos has been sending us mysterious flashes of ultra-bright blue light that appear out of nowhere and disappear in a matter of days. This phenomenon has a strange little name, but they are known as ‘luminous fast blue optical transients’ (LFBOTs), and have baffled astronomers since its discovery. Now, thanks to the analysis of one that has become the brightest ever detected, scientists believe they have solved the enigma: they are black holes devouring companion stars, and the process is extremely violent.

The discovery. The team led by researchers from the University of California at Berkeley analyzed a LFBOT discovered in 2024 and named ‘AT 2024wpp’. The phenomenon turned out to be between five and ten times more luminous than any other of its kind previously observed. Astronomers used a range of space and ground-based telescopes (including Chandra, Swift, NuSTAR, ALMA, and the Keck and Gemini observatories) to study it at multiple wavelengths, from X-ray to radio.

The data revealed that the energy released by AT 2024wpp was 100 times greater than that of a normal supernova. As Natalie LeBaron, a graduate student at Berkeley and first author of one of the studies, explains, “the absolute amount of energy radiated by these bursts is so large that you can’t feed them with the collapse and explosion of a massive star, or with any other type of normal stellar explosion.”

An extreme cosmic feast. The researchers they propose that these flashes are produced by what they call “extreme tidal disruption.” This process occurs when a black hole (with a mass up to 100 times that of our Sun) completely destroys its companion star in a matter of days. According to the team’s reconstructions, the black hole had been absorbing material from its companion for a long time, surrounding itself with a halo of gas.

In the case studied, the scientists report that, when the star got too close and was torn apart, the new material violently collided with the pre-existing gas as it fell towards the black hole, generating the intense blue and ultraviolet light characteristic of LFBOTs.

According to account Robert Sanders, a researcher at the University of Berkeley, Some of the gas was ejected in jets from the poles of the black hole at about 40% of the speed of light, producing the radio emissions that scientists later detected.

Intermediate mass black holes, a separate enigma. The black hole’s inferred mass places these objects in a particularly interesting category: intermediate-mass black holes. Although experiments like LIGO Black hole mergers of more than 100 solar masses have been detected, they have never been directly observed and their formation process remains a mystery.

“Theorists have proposed many ways to explain how we get these large black holes,” points out Raffaella Margutti, associate professor of astronomy and physics at Berkeley and lead author of both studies. “LFBOTs allow us to approach this question from a completely different angle. They also allow us to characterize the precise location where these things occur within their host galaxy, which adds more context to trying to understand how we ended up with this configuration: a very large black hole and a companion.”

A family of phenomena with curious nicknames. The first LFBOT with sufficient data for analysis was detected in 2018 and received the official designation ‘AT 2018cow’. His name led researchers to nickname him “the Cow”, a tradition that continued with later events: the Koala, the Tasmanian Devil and the Finch. AT 2024wpp, the subject of this study, has already been informally named the Woodpecker.

To date, just over a dozen of these events have been identified, all located in galaxies with active star formation at distances of hundreds of millions and billions of light years. The companion star destroyed in AT 2024wpp was more than 10 times the mass of the Sun and could have been a Wolf-Rayet starthat is, very hot and evolved objects that have already consumed much of their hydrogen.

TO hunting for LFBOTs. Researchers hope that the upcoming ultraviolet space telescopes, ULTRASAT and UVEX, scheduled to launch in the coming years, will revolutionize the detection of these phenomena. “Right now we find only one LFBOT a year or so. But once we have UV telescopes in space, finding LFBOTs will become routine, like detecting gamma ray bursts today,” explains Nayana AJ, researcher at Berkeley and first author of X-ray and radio analysis.

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