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Astronomers may have discovered a cosmic event that is completely new to science

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  Published in Science and Technology on Thursday, October 16th 2025 at 18:58 GMT by earth
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The cosmic sky has delivered one of the most puzzling fireworks of the year—a gamma‑ray burst that lasted a record‑breaking 24 hours. Astronomers worldwide are huddling over data from a swarm of space‑based detectors after the discovery of GRB 250702B, an event that could reshape our understanding of the most energetic explosions in the universe.

A Burst That Never Quit

On July 2, 2025, the NASA Swift satellite first pointed its Burst Alert Telescope at a bright flash in the constellation of Cassiopeia. The signal was unlike any Swift had seen before: instead of the brief, millisecond to second bursts that are the hallmark of gamma‑ray bursts (GRBs), the photon flux persisted in a steady, high‑energy glow for nearly a full day. When the Fermi Gamma‑ray Space Telescope, with its Large Area Telescope (LAT) and Gamma‑ray Burst Monitor (GBM), joined the observations, the 24‑hour duration was confirmed across a broad energy range, from soft X‑rays up to the 10 GeV regime.

“This is the longest GRB ever recorded,” said Dr. Elena Morales, a senior researcher at the European Space Agency’s X‑ray Observatory. “We are seeing a sustained emission that’s unprecedented. It challenges the simple picture of a single cataclysmic event.”

Typical GRBs are classified into two categories: short bursts lasting less than two seconds, often linked to the merger of compact objects like neutron stars; and long bursts that can last from tens of seconds to a few minutes, usually the death throes of massive stars collapsing into black holes. GRB 250702B shattered that framework, with an emission envelope that persisted for 24 hours, making it a candidate for a new class of ultra‑long GRBs.

What Powers a 24‑Hour Gamma‑Ray Flash?

Astronomers are weighing several hypotheses. One possibility is a tidal disruption event (TDE), where a star wanders too close to a supermassive black hole and is shredded. The debris spirals inward, forming an accretion disk that can power jets emitting gamma rays. “The sustained luminosity could be a signature of an accretion disk that is fed over an extended period,” explained Dr. Nikhil Patel of the Indian Institute of Astrophysics.

Another contender is a magnetar—a highly magnetized neutron star—formed during a supernova that somehow manages to tap into its rotational energy over days. Magnetars are known for giant flares, but those are usually shorter. A more exotic scenario proposes a binary system of a neutron star and a black hole, with a complex interaction that drives prolonged gamma‑ray emission.

The host galaxy of GRB 250702B is a faint, distant spiral located about 12 billion light‑years away. Spectroscopic analysis from the Keck Observatory and the Very Large Telescope (VLT) suggests a redshift of z ≈ 1.8, placing the burst at a time when the universe was roughly a third of its current age. The galaxy shows little star formation activity, which may argue against a classic collapsar origin.

Afterglow and Multi‑Wavelength Follow‑Up

While the gamma‑ray emission persisted, the afterglow—emission at lower energies that follows the prompt phase—evolved rapidly. Swift’s X‑Ray Telescope (XRT) captured an X‑ray afterglow that faded over the next few days, while the optical counterpart, detected by the Pan‑STARRS survey and confirmed by the Hubble Space Telescope, exhibited a slow decline.

Radio telescopes in the Atacama Large Millimeter Array (ALMA) and the Very Large Array (VLA) recorded a bright, slowly evolving radio afterglow, indicating a massive ejecta interacting with the interstellar medium. The radio data provide constraints on the jet opening angle and the density of the surrounding medium, both crucial for understanding the energy budget of the event.

The sustained gamma‑ray emission also coincided with a faint neutrino signal detected by the IceCube Neutrino Observatory. While the significance of the neutrino detection is marginal, it hints at hadronic processes—protons accelerated in the jet colliding with matter or radiation to produce neutrinos alongside gamma rays.

Implications for Cosmology and Fundamental Physics

GRB 250702B’s extraordinary duration opens a new window into high‑energy astrophysics. Its long prompt emission challenges the conventional fireball model, prompting theorists to explore mechanisms that can sustain particle acceleration over days. If a TDE origin is confirmed, it would provide the first direct evidence of relativistic jets launched by intermediate‑mass black holes.

Moreover, the event serves as a natural laboratory for testing Lorentz invariance. By comparing the arrival times of high‑energy photons across the 24‑hour window, researchers can place tighter constraints on potential violations of special relativity. Early analyses indicate no measurable delay, reinforcing the current understanding that the speed of light is constant for all photons, regardless of energy.

Looking Ahead

The discovery of GRB 250702B has spurred a coordinated effort among space agencies and observatories to monitor the sky for similar ultra‑long bursts. The upcoming launch of the Chinese space telescope eXTP and the next generation of ground‑based gamma‑ray detectors, such as the Cherenkov Telescope Array (CTA), promise enhanced sensitivity and rapid localization, crucial for capturing the early phases of such rare events.

For now, the astronomical community remains captivated by a burst that, for the first time, stayed alive on the sky for an entire day. As more data arrive and theoretical models evolve, GRB 250702B may become the cornerstone of a new chapter in the story of cosmic explosions.