Black Hole Eats Star: Merger Animation | NASA Science
Astronomers have been poring over a flood of data from NASA satellites and other facilities as they try to work out what was responsible for an extraordinary cosmic outburst discovered on July 2, 2025. The event was a gamma-ray burst (GRB), the most powerful class of cosmic explosions. However, while most GRBs last only a minute, this one continued for days. Named GRB 250702B, the burst's record-setting duration places it in a class by itself. The initial wave of gamma rays lasted at least 7 hours, nearly twice the duration of the previous record holder.
This animation illustrates a proposed explanation for the origin of GRB 250702B, one preferred by the team studying the burst's gamma-ray features. Their model envisions a black hole weighing about three times the Sun—with an event horizon just 11 miles (18 kilometers) across—orbiting and merging with a companion star. The star is of similar mass to the black hole but is much smaller than the Sun. This is because its hydrogen atmosphere has mostly been stripped away, down to its dense helium core, forming an object astronomers call a helium star.
Matter from the star first flows toward the black hole and collects into a vast disk, from which the gas makes its final plunge. At a point in this process, the system begins to shine brightly in X-rays. Once the black hole is totally immersed within the main body of the star, feasting on it from within, gamma-ray jets blast outward. This energy released within the star causes it to explode, producing a supernova—a unique prediction of the helium merger model. Unfortunately, no supernova was observed to follow GRB 250702B, perhaps due to obscuring dust and the vast distance, so alternative scenarios cannot be ruled out.
Detected about once a day on average, GRBs can appear anywhere in the sky with no warning. They are very distant events with the closest-known example erupting more than 100 million light-years away.
Most bursts last from a few milliseconds to a few minutes and are known to form in two ways, either by a merger of two city-sized neutron stars or the collapse of a massive star once its core runs out of fuel. Each produces a new black hole. Some of the matter falling toward the black hole becomes channeled into tight jets of particles that stream out at almost the speed of light, creating gamma rays as they go. Nevertheless, neither of these types of bursts can readily create jets able to fire for days. This is why 250702B poses a unique puzzle.
Animator: Brian Monroe
Producer: Scott Wiessinger (eMITS)
Science Writer: Francis Reddy (University of Maryland College Park)
Scientist: Eric Burns (LSU)
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