Deep space signal that lasted 25,200 seconds gets a possible explanation

A blast from deep space that lasted for seven hours surprised astronomers in 2025. It was a signal coming from some intensely active region. Designated GRB 250702B, it was first detected in the 1960s by the US military. However, over the years, as technology developed, instruments detected more of them. This signal intrigued scientists because of how long it lasted. Typically, these bursts can go from a few milliseconds to several minutes. The longest burst before GRB 250702B was recorded last year and was 15,000 seconds long. GRBs largely have two points of origin - Supernovae or Kilonovae. The former occurs when a star spiralling at extreme speeds falls into a black hole, while the latter occurs when two ultra-dense neutron stars collide and merge.

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But none of them would have produced high-energy jets for seven hours, or 25,000 seconds. So scientists started searching for the origin, and what could have caused such a long signal. For starters, they knew that the reason had to be something new since GRB 250702B shattered standard physics models. Astrophysicists and researchers from NASA’s Goddard Space Flight Center collected all the data, including from ground instruments like the European Southern Observatory's Very Large Telescope. They noted that the culprit was possibly a rare "helium merger."

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Helium star locked with a black hole

They theorised that a binary system was where it originated, where a stellar-mass black hole was locked in a tight orbit with a helium star, one that has already shed its outer layers of hydrogen, and is merely a highly dense helium core. As the helium star naturally aged and expanded, the black hole drifted inside the star's outer envelope. It rapidly consumed the dense helium star from the inside out, and this led to a huge amount of rotational energy being transferred to the black hole. A high-energy jet was unleashed that could fire gamma rays for seven hours. NASA is now preparing to study more stellar deaths.