What Powers the Universe's Brightest Blue Flashes Is Worse Than a Supernova

For roughly a decade, astronomers have been noticing brief, extraordinarily bright flashes of blue and ultraviolet light blazing across the sky and then vanishing, leaving behind faint X-ray and radio emissions. Fewer than 15 have been catalogued to date, and astrophysicists have argued over the mechanism ever since: an exotic supernova variant, or gas accreting onto a black hole. The answer, it turns out, is neither. The answer is considerably more violent.

UC Berkeley researchers determined that LFBOTs — luminous fast blue optical transients, as the phenomenon is formally classified — result from an extreme tidal disruption, in which a black hole reaching up to 100 solar masses tears apart its massive stellar companion over the course of days. The word "tears" is doing a great deal of work in that sentence, and it earns every bit of it.

One LFBOT discovered last year, AT 2024wpp, provided the data needed to narrow down the origins of these bursts. For the first time, researchers confirmed that LFBOTs require some sort of central energy source beyond what a supernova can produce on its own. AT 2024wpp radiated 100 times the energy of a normal supernova in its first 45 days. Roughly 24 days after the explosion, the Keck Observatory detected an unusual excess of near-infrared light, only the second time such a feature has been observed in this rare class of events. That mass range — loosely grouped under the label intermediate-mass black holes — opens its own set of questions for the field.

Current surveys deliver about one LFBOT a year, which is hardly enough for a census. Two upcoming missions, ULTRASAT and UVEX, will bring dedicated wide-field ultraviolet observatories to bear on the problem in the coming years.

A black hole 100 times the mass of our sun, quietly paired with a massive star companion, waiting. The star never stood a chance.

Read the full story at Berkeley News, December 16, 2025

Hot Take: A decade of astronomers debating "unusual supernova or gas accretion" while the actual answer was "black hole tears its own companion star apart in a matter of days" is a useful reminder that when the universe decides to be dramatic, it does not consult the shortlist of tidy explanations we had prepared for it.