Gamma-ray burst explodes in an unusual pattern never seen before

The night sky often dazzles with brief explosions of unimaginable power. Gamma-ray bursts are among the most intense, usually marking the catastrophic end of stars. These bursts vanish within seconds or minutes, leaving astronomers with little more than fleeting traces.

But a recent observation broke every rule. One gamma-ray burst not only lasted far longer than usual but also repeated in a pattern that has never been recorded before.

Astronomers stunned by burst

The burst, labeled GRB 250702B, was reported in The Astrophysical Journal Letters. Dr. Antonio Martin-Carrillo and colleagues used the European Southern Observatory’s Very Large Telescope to study the phenomenon.

“This event is unlike any other seen in 50 years of GRB observations,” said Dr. Martin-Carrillo of the University College Dublin. “GRBs are catastrophic events, so they are expected to go off just once because the source that produced them does not survive the dramatic explosion.”

“This event baffled us not only because it showed repeated powerful activity but also because it seemed to be periodic, which has never seen before.”

Star collapse or black hole?

Theories about its origin vary. One possibility involves the collapse of a star many times more massive than the Sun. In such a case, some material could have continued feeding the central engine, extending its activity.

Another explanation suggests a tidal disruption event, where a star is torn apart by a black hole.

For this burst, the data hint that a white dwarf might have been shredded by an intermediate-mass black hole – a long-hypothesized but rarely seen type.

A burst that wouldn’t end

Most gamma-ray bursts last milliseconds to minutes. This one endured about a day – hundreds of times longer than the norm.

Professor Andrew Levan of Radboud University noted that it was 100 to 1,000 times longer than most GRBs.

The unusual length led astronomers to compare it with ultralong bursts and even with rare tidal disruption events.

However, GRB 250702B showed distinct bursts at intervals that seemed close to integer multiples, hinting at possible periodic behavior.

Pinpointing the source

Initial detections came from NASA’s Fermi Gamma-ray Space Telescope and the Chinese Academy of Sciences’ Einstein Probe.

Both caught early signals but could not locate the source precisely. The Very Large Telescope provided sharper data, showing the event was located outside of our galaxy.

“The event seemed to have originated from within our galaxy due to its proximity to the galactic plane. The VLT fundamentally changed that paradigm,” Professor Levan noted.

Host galaxy revealed

The HAWK-I camera on the VLT revealed an extremely red infrared counterpart, suggesting a heavily dust-obscured source.

Follow-up imaging with the Hubble Space Telescope confirmed the host galaxy’s structure. Observations showed the galaxy had a complex, asymmetric shape, possibly with dust lanes. Such dust could explain the unusually red afterglow.

“What we found was considerably more exciting – the fact that this object is extragalactic means that it is considerably more powerful,” said Dr. Martin-Carrillo.

Collision explains the glow

The afterglow in X-ray, infrared, and radio wavelengths appeared consistent with models in which relativistic jets collide with surrounding material.

Yet the details pointed to an unusually narrow jet angle and significant dust extinction, unlike most known bursts.

Despite these differences, the afterglow fit within the broader family of GRB models, strengthening the case for either a rare stellar collapse or a tidal disruption event involving a black hole.

Mystery sparks new theories

The researchers outlined four possible scenarios. First, it may have been a relativistic tidal disruption event, most likely a white dwarf consumed by an intermediate-mass black hole.

The second possibility is a nonstandard stellar collapse involving unusual progenitors or environments. Third, the event may have been echoes caused by the scattering of gamma rays through dense dust shells.

A fourth possibility is that the burst came from a very distant, high-redshift source and was brightened by gravitational lensing. Each theory presents challenges, but the first two currently align best with the data.

Clarifying the gamma-ray burst

“We are still not sure what produced this or if we can ever really find out but, with this research, we have made a huge step forward towards understanding this extremely unusual and exciting object,” said Dr. Martin-Carrillo.

Future monitoring with instruments like the James Webb Space Telescope may offer more clues. Continued X-ray and radio tracking could reveal whether the burst’s jet shuts down like those in tidal disruption events or follows the path of an unusual star’s collapse.

Either way, GRB 250702B has already reshaped what astronomers thought they knew about cosmic explosions.

The study is published in The Astrophysical Journal Letters.

Image Credit: NASA, ESA and M. Kornmesser

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–