An intense, sudden burst of brilliant light in the cosmos might be the result of a black hole consuming a massive star that has shed its external gas layers.
Back in 2018, astronomers identified a novel cosmic eruption. This event, designated AT2018cow and nicknamed “the Cow,” rapidly escalated to its peak luminosity in mere days. This acceleration stood in stark contrast to typical supernovae, which require weeks to reach their brightest point.
The initial cause of this rapid outburst remained unclear. In the years following the Cow’s discovery, only a small number of similar events have been observed. These are collectively known as fast blue optical transients, or FBOTs, and their origin continues to be a puzzle.
A Brighter Encounter: The Whippet’s Signal
Researchers, including Jialian Liu from Tsinghua University in China, propose that a recent cosmic flash—the most luminous FBOT recorded to date—likely stems from an unusual star. This star, estimated to be more than 30 times the mass of our sun, had already lost its outer hydrogen layers. A black hole then apparently consumed this exposed stellar core.
This particular event, named AT 2024wpp and referred to as “the Whippet,” was first detected by the Zwicky Transient Observatory at the close of 2024. It swiftly intensified, becoming approximately ten times brighter than the previously observed Cow event. Liu and his team utilized multiple telescopes, including the Swift X-Ray Telescope and the Australia Telescope Compact Array, in the weeks after its initial detection. This allowed them to gather comprehensive data on the light emitted across various wavelengths.
The spectrum analysis of the light indicated that the explosive event responsible was over six times hotter than the sun’s surface. Additionally, plasma was ejected at a speed close to one-fifth of the speed of light. A significant finding was the detection of a secondary burst of X-rays about a month after the initial light emission, a phenomenon not previously observed in any other FBOT.
Explaining the Phenomenon: A Wolf-Rayet Star’s Demise
Liu and his colleagues suggest that the most plausible explanation for these combined observations involves an uncommon type of star known as a Wolf-Rayet star. These stars are characterized by their exposed stellar cores, lacking an outer gaseous envelope. The researchers theorize that the Whippet event resulted from such a star being consumed by a black hole approximately 15 times the mass of our sun.
The initial collision between the star and the black hole likely generated the first burst of light. Subsequently, some of the star’s remaining material, which had been orbiting the black hole, may have spiraled back inward, leading to the release of the second X-ray burst. Ashley Crimes at the European Space Agency considers this a compelling explanation, noting that among the various hypotheses, “this one probably has the least problems.”
Environmental Clues: Young Galaxies and Extreme Stars
One of the most persuasive pieces of evidence supporting this scenario is the observed origin of the event: a young galaxy. Crimes points out that such environments are more conducive to the existence of short-lived, extreme stars like Wolf-Rayet stars. “These are the kinds of environments that you’d expect to see this kind of event,” he stated. “And then, in addition, you see this bump at late times, which could be material falling back after a merger. It’s promising.”