Astronomers have noticed a cosmic explosion of high-energy gamma-rays in contrast to any ever seen earlier than. The gamma-ray burst (GRB) designated GRB 250702B set itself aside from different explosive bursts of gamma-rays by exploding a number of occasions in at some point.
That is one thing troublesome to elucidate, given GRBs are thought to come up from the catastrophic deaths of huge stars, with no identified situation at present accounting for repeated blasts over a full day. Co-lead researcher and College School Dublin astronomer, Antonio Martin-Carrillo, mentioned in an announcement that this GRB is “in contrast to every other seen in 50 years of GRB observations.“
GRB 250702B was initially detected by NASA’s Fermi Gamma-ray House Telescope on July 2, 2025, however its location was unsure. The next day, GRB 250702B was investigated by the Very Giant Telescope (VLT), which used its HAWK-I infrared digital camera to pinpoint the supply of this GRB exterior the Milky Manner. This was later confirmed by the Hubble House Telescope.
GRBs are believed to happen both when huge stars attain the tip of their lives and bear gravitational collapse to turn out to be black holes or neutron stars, or when an unlucky star wanders too near a black gap and is shredded in a so-called “tidal disruption occasion.”
This results in what are at present considered probably the most energetic explosions in the universe, placing out as a lot vitality in a interval starting from milliseconds to minutes because the solar will radiate in round 10 billion years.
GRB 250702B, alternatively, lasted round a day. That’s 100 to 1,000 occasions longer than most GRBs, in accordance with co-team chief and Radboud College researcher Andrew Levan.
“Extra importantly, gamma-ray bursts by no means repeat for the reason that occasion that produces them is catastrophic,” Martin-Carrillo added.
When Fermi initially noticed GRB 250702B on July 2, the house telescope noticed it burst 3 times over a number of hours. Then, an examination of knowledge from the Einstein Probe X-ray house telescope revealed that the identical supply had erupted a day prior. This makes GRB 250702B a long-period repeating GRB like nothing astronomers have beforehand noticed. Its nature stays a thriller.
“If it is a huge star, it’s a collapse in contrast to something we have now ever witnessed earlier than,” Levan mentioned.
Fermi and the Einstein Probe couldn’t pinpoint the supply of GRB 250702B, with the explosion showing to have come from the airplane of our personal galaxy, the Milky Manner. To verify or refute this, the group turned to the VLT, one of many world’s most superior optical telescopes positioned on the Paranal Observatory within the Atacama Desert of northern Chile.
“Earlier than these observations, the final feeling locally was that this GRB should have originated from inside our galaxy,” Levan mentioned. “The VLT essentially modified that paradigm.”
Observations made with the HAWK-I digital camera confirmed that GRB 250702B really erupted past the boundaries of the Milky Manner, in one other galaxy. This was then confirmed by Hubble.
The precise distance to the supply of GRB 250702B is not sure but, however the group thinks that the scale and brightness of its house galaxy point out it’s positioned billions of light-years away.
“What we discovered was significantly extra thrilling: the truth that this object is extragalactic implies that it’s significantly extra highly effective,” Martin-Carrillo mentioned.
Additional investigation of GRB 250702B shall be wanted to each extra precisely pinpoint its location and to find out what brought on this long-lasting repeating blast of gamma-rays.
One rationalization can be a large star collapsing onto itself, releasing huge quantities of vitality. This could have created a GRB lasting mere seconds, nonetheless. Alternatively, a star being ripped aside in TDE may produce a day-long GRB, however this situation fails to copy different properties of the GRB 250702B, an explosion that might require a really uncommon star being destroyed by a fair stranger black gap.
The group is at present monitoring the location of this explosion with the VLT and the James Webb House Telescope, hoping to catch a glimpse of its aftermath to raised perceive its nature.
“We’re nonetheless undecided what produced this, however with this analysis, we have now made an enormous step ahead in the direction of understanding this extraordinarily uncommon and thrilling object,” Martin-Carrillo concluded.
The group’s analysis was revealed on Aug. 29 in The Astrophysical Journal Letters.
