If you’ve been following Gizmodo’s astrophysics coverage, you’ve probably noticed a pattern: Scientists study a cosmic phenomenon and start to get a handle on it—then something shows up that completely upends their understanding. The latest example? It’s explosive. Literally.
Gamma-ray bursts (GRBs) are the most powerful explosions in the universe. Generally, GRBs last from milliseconds to several minutes. Scientists believe they emerge when massive stars explode in supernovas or get ripped apart by black holes. But GRB 250702B, the newly observed signal, is “unlike any other seen in 50-years of GRB observations,” said Antonio Martin-Carillo, co-lead author of a study describing the discovery published recently in The Astrophysical Journal Letters, in a statement.
GRB 250702B lasted for about a day—an unusually long duration for a phenomenon like this. Astronomers believe that its source is a galaxy about a few billion light-years away, but that’s just about all they know right now about a potential source.
Too long to be true
GRBs are short-lived because “the event that produces them is catastrophic,” Martin-Carillo, an astronomer at University College Dublin in Ireland, said. It therefore doesn’t make a lot of sense for the same (already “dead”) source to create repeated bursts.
That’s why GRB 250702B is so confusing. This odd burst, first captured by NASA’s Fermi Gamma-ray Space Telescope, arrived at Earth not once but three times over the course of several hours, which made its lifespan already record-breakingly long. Later, when researchers with Fermi compared notes with the Einstein Probe team, the astronomers were shocked to learn that the same source had actually been active nearly a full day earlier.
If that wasn’t surprising enough, the researchers now think the powerful radiation detected from GRB 250702B may actually be weaker than its true form. At first, they believed it came from within our own galaxy, but follow-up observations with the Hubble Space Telescope suggest it originated much farther out in the universe.
“What we found was considerably more exciting: the fact that this object is extragalactic means that it is considerably more powerful,” said Martin-Carrillo.
Stars only live once…?
Cosmic entities are remarkably durable, but even stars aren’t exempt from the rule that death only strikes once. So, if GRB 250702B originated from a massive star collapsing into itself, which is the going theory for GRBs in general, “it is a collapse unlike anything we have ever witnessed before,” said Andrew Levan, paper co-lead author and an astronomer at Radboud University in The Netherlands, in the same release.
Still, a star collapse as we know it should have created a GRB that lasted for only a few seconds. Theoretically, a star being ripped to shreds by a black hole could generate a day-long GRB. But for this hypothesis to hold, it would require an unusually strange black hole gobbling up an equally strange star—a scenario that’s theoretically possible, but one the researchers aren’t yet able to confirm.
A plausible scenario proposed by the researchers involves a white dwarf—a stellar core left over from a dead star—that became a victim of an intermediate black hole, a rare, poorly understood class of black holes. Both demonstrate some odd gravitational behavior that astronomers have yet to fully investigate, so that’s where the missing link could be, the researchers said.
“We are still not sure what produced this, but with this research we have made a huge step forward towards understanding this extremely unusual and exciting object,” Martin-Carrillo said.