Tracking the Fading Afterglow

Building on earlier findings, a research team led by Jonathan Carney, a graduate student at the University of North Carolina at Chapel Hill, set out to closely monitor the burst’s afterglow—the slowly fading light that follows the initial, extremely bright gamma-ray flash. By studying how this emission evolves over time, scientists can better understand the physical mechanisms responsible for producing gamma-ray bursts.

Figure 1. Record-Setting Gamma-Ray Explosion Shone for 7 Hours.

The Blanco Telescope is located at NSF’s Cerro Tololo Inter-American Observatory (CTIO) in Chile, while the International Gemini Observatory operates two telescopes—Gemini North in Hawai‘i and Gemini South in Chile. The observatory is partially funded by the National Science Foundation and operated by NSF NOIRLab. Figure 1 shows Record-Setting Gamma-Ray Explosion Shone for 7 Hours

This video opens on the star-filled region surrounding the host galaxy of GRB 250702B, the longest gamma-ray burst ever recorded by astronomers.

“The ability to rapidly reposition the Blanco and Gemini telescopes on short notice is essential for capturing fleeting events like gamma-ray bursts,” says Carney. “Without this capability, our understanding of distant, rapidly changing phenomena in the night sky would be far more limited.”

For their study, the team employed a powerful set of instruments: the NEWFIRM wide-field infrared imager and the 570-megapixel Dark Energy Camera (DECam), both installed on the Blanco Telescope, along with the Gemini Multi-Object Spectrographs (GMOS) on the Gemini North and Gemini South telescopes.

Peering Through Cosmic Dust

Analysis of the observations showed that GRB 250702B was invisible in optical light, due in part to dust within our own Milky Way, but even more so because of heavy dust obscuration in the burst’s host galaxy. Gemini North provided the only detection close to visible wavelengths, requiring nearly two hours of exposure time to extract the faint signal hidden beneath thick layers of dust.

Carney and his colleagues combined these observations with new data from the Keck I Telescope at the W. M. Keck Observatory, along with publicly available observations from the Very Large Telescope (VLT), NASA’s Hubble Space Telescope, and multiple X-ray and radio observatories. This comprehensive dataset was then compared with theoretical models—frameworks used to explain and predict the behavior of astronomical phenomena—allowing the team to refine their interpretation of the event.

A Relativistic Jet in a Dense Environment

The team’s analysis indicates that the initial gamma-ray emission likely originated from a narrow, extremely fast-moving stream of material known as a relativistic jet, which slammed into dense material surrounding offering a clue to the explosion’s unusual properties. Their findings also reveal important details about the GRB’s environment and host galaxy: an unusually large amount of dust near the burst location and a host galaxy that is far more massive than those typically associated with gamma-ray bursts.

Together, the data support a scenario in which GRB 250702B occurred within a dense, dusty region—possibly a thick dust lane within the host galaxy that lies directly along our line of sight. These environmental insights place strong constraints on the nature of the system that produced this extraordinary, record-breaking gamma-ray explosion.

Of the approximately 15,000 gamma-ray bursts detected since the phenomenon was first identified in 1973, only a handful—fewer than six—approach the extraordinary duration of GRB 250702B. Proposed explanations for these ultra-long events have included the collapse of a blue supergiant star, a tidal disruption event, or the birth of a highly magnetized neutron star known as a magnetar. GRB 250702B, however, does not fit cleanly into any of these established categories.

Possible Origins of a Record-Breaker

Based on the data collected so far, scientists have identified several plausible origin scenarios. One possibility involves a black hole plunging into a star that has already lost its hydrogen envelope and now consists almost entirely of helium. Another scenario envisions a star—or even a sub-stellar object such as a planet or brown dwarf—being torn apart during a close encounter with a compact object like a stellar-mass black hole or a neutron star, an event known as a micro–tidal disruption. A third, more dramatic possibility is a star being shredded as it falls into an intermediate-mass black hole, a class of black holes thought to be common but notoriously difficult to observe, with masses between one hundred and one hundred thousand times that of the Sun. If this final scenario proves correct, it would mark the first-ever observation of a relativistic jet produced as an intermediate-mass black hole consumes a star.

Although additional observations are needed to pinpoint the true origin of GRB 250702B, the data gathered so far are consistent with these unconventional explanations.

“This work presents a fascinating cosmic archaeology puzzle, where we’re reconstructing the details of an event that unfolded billions of light-years away,” says Carney. “Unraveling mysteries like this shows just how much we still have to learn about the Universe’s most extreme phenomena—and reminds us to keep imagining what might be happening out there.”

Source: SciTECHDaily

Cite this article:

Priyadharshini S (2025), Unprecedented Gamma-Ray Explosion Lasted 7 Hours, Baffles Scientists, AnaTechMaz, pp.646