Black Hole ‘Spaghettification’ Solves Decade-Long Mystery of Fast Blue Optical Transients
New observations of the brightest such event ever recorded reveal these cosmic flashes aren’t supernovae, but the dramatic destruction of a star by a black hole.
For years, astronomers have puzzled over luminous fast blue optical transients (LFBOTs) – incredibly bright, short-lived bursts of energy. Now, a groundbreaking analysis of the most luminous LFBOT discovered to date, designated AT 2024wpp, has revealed their true origin: a black hole violently shredding a star in a tidal disruption event. This discovery, published in two forthcoming papers in The Astrophysical Journal Letters, resolves a decade-long debate and offers new insights into the extreme physics governing black holes and stellar evolution.
LFBOTs, first observed in 2014 with the initial well-analyzed event AT 2018cow nicknamed “the Cow,” are characterized by their intense blue light and rapid fade. These enigmatic phenomena, appearing over distances of hundreds of millions to billions of light-years, have been difficult to categorize. Were they a new type of supernova, or something else entirely?
The answer, according to a team led by researchers at the University of California, Berkeley, is neither. AT 2024wpp, discovered in 2024, emitted energy 100 times greater than a typical supernova, requiring the conversion of roughly 10% of the Sun’s mass into energy in a matter of weeks. “The sheer amount of radiated energy from these bursts is so large that you can’t power them with a core collapse stellar explosion — or any other type of normal stellar explosion,” explains Natalie LeBaron, a UC Berkeley graduate student and first author on one of the papers. “The main message from AT 2024wpp is that the model that we started off with is wrong. It’s definitely not just an exploding star.”
Crucial to this breakthrough were observations from the International Gemini Observatory, funded in part by the U.S. National Science Foundation, and specifically data collected with the Flamingos-2 instrument on the Gemini South telescope in Chile. These observations revealed an unexpected excess of near-infrared light, a signature previously observed only in AT 2018cow and now established as a hallmark of LFBOTs.
The team’s analysis suggests a scenario where a black hole, potentially up to 100 times the mass of our Sun, had been slowly siphoning material from a companion star for an extended period. This created a halo of material surrounding the black hole. When the companion star ventured too close, it was torn apart in a dramatic tidal disruption event. The resulting debris formed a swirling accretion disk around the black hole, generating intense X-ray, ultraviolet, and blue light as the material collided.
Furthermore, a significant portion of the shredded star’s gas was ejected as powerful jets from the black hole’s poles, traveling at approximately 40% of the speed of light and emitting radio waves as they interacted with surrounding gas. “The ongoing discovery of luminous fast blue optical transients shows that Gemini South and other ground-based astronomical facilities are primed to characterize these mysterious objects,” says Martin Still, NSF program director for the International Gemini Observatory. “We expect the NSF–DOE Vera C. Rubin Observatory will spot large numbers of these transient objects, giving Gemini and other telescopes unprecedented opportunities for detailed follow-up observations.”
AT 2024wpp, located 1.1 billion light-years away, is between 5 and 10 times more luminous than AT 2018cow. The shredded star is estimated to have been more than 10 times the mass of the Sun, and may have been a Wolf-Rayet star – a hot, evolved star that has already shed much of its hydrogen. This would explain the weak hydrogen emission detected from the event.
The discovery not only solves a long-standing mystery but also highlights the diversity of catastrophic events that can occur in the universe. As astronomers continue to observe these fleeting phenomena, they hope to refine their understanding of black hole physics and the ultimate fate of stars. Perhaps, as researchers playfully suggest, AT 2024wpp will be known as “the Wasp,” joining the ranks of previous LFBOTs affectionately nicknamed “the Cow,” “the Koala,” “the Tasmanian devil,” and “the Finch.”
