James Webb Telescope Unveils GRB 250702B — The Longest Gamma-Ray Burst Ever
JWST Discovery Today - James Webb Telescope Unveils GRB 250702B — The Longest Gamma-Ray Burst Ever
James Webb Telescope Unveils GRB 250702B — The Longest Gamma-Ray Burst Ever
James Webb Space Telescope captures the clearest-ever view of GRB 250702B’s distant host galaxy—an 8-billion-year-old light signal shining through a dark dust lane, revealing the true location of the record-breaking gamma-ray burst. Credit: NASA, ESA, CSA, H. Sears (Rutgers). Image processing: A. Pagan (STScI)
Updated on: December 08, 2025 | By: Jameswebb Discovery Editorial Team
An unprecedented cosmic explosion lasting over seven hours reveals a new class of stellar destruction — and the James Webb Space Telescope (JWST) provides the clearest view yet.
On July 2, 2025, astronomers around the world detected one of the most extraordinary cosmic explosions ever observed. Known as GRB 250702B, this gamma-ray burst smashed every previous record — not with its brightness, but with its unbelievable duration.
While typical gamma-ray bursts (GRBs) last seconds to minutes, this one continued for over seven hours and emitted unusual flares for days. With more than 15,000 GRBs recorded since 1973, none have lasted as long — making GRB 250702B a once-in-a-lifetime event.
And at the heart of this discovery lies the powerful vision of the James Webb Space Telescope, whose unprecedented infrared resolution finally revealed the mysterious host galaxy behind thick cosmic dust.
This historic event is more than an anomaly — it may represent a new kind of stellar explosion and a new way black holes consume stars.
GRB 250702B did not behave like any previously known gamma-ray burst. NASA scientists confirmed:
The initial gamma-ray wave lasted at least seven hours
X-ray activity flared for up to two days
Signals appeared even a full day before peak emission
No standard GRB model can explain its longevity
According to Eliza Neights of George Washington University and NASA Goddard:
“This is certainly an outburst unlike any other we’ve seen in the past 50 years.”
Its extreme properties immediately suggested something more exotic than the two known GRB types:
Usually lasts seconds to minutes.
Produces short bursts.
Neither of these mechanisms can sustain jet emissions for hours, much less days — which means GRB 250702B likely represents an entirely new phenomenon.
Astronomers now agree the most probable cause was a black hole eating a star — but there are two competing models.
A “middleweight" black hole — one with a few thousand times the mass of the Sun — may have shredded a star that wandered too close. This rare event is called a tidal disruption event (TDE).
Key features supporting this scenario:
An intermediate black hole can produce long-lived jets
A passing star would be consumed in roughly one day
The extreme duration fits theoretical predictions
However, this type of black hole is extremely difficult to find and rarely observed.
This model, supported by the gamma-ray analysis team, fits the GRB signature even better.
In this scenario:
A black hole three times the mass of the Sun orbited a helium-rich companion star
It spiraled inward, stripping gas and creating blazing X-ray emissions
When the black hole entered the star’s core, it consumed material rapidly
This unleashed powerful gamma-ray jets lasting hours
The final energy release exploded the star from within
This merger would produce X-rays before and after the main burst — exactly what NASA observed.
Although a supernova should have followed, thick dust and extreme distance likely hid it from even the James Webb Telescope.
No single instrument could fully observe the burst. Instead, NASA’s space fleet formed a coordinated network across multiple wavelengths:
Fermi Gamma-ray Space Telescope
Swift Observatory
Wind / Konus
Psyche spacecraft (GRNS)
Japan’s MAXI on the ISS
These detectors captured the GRB’s unusual repeated triggers, its multi-hour emission, and its early faint signals.
Swift XRT
Chandra X-ray Observatory
NuSTAR
NuSTAR and Swift identified dramatic X-ray flares for 48 hours, proof that the black hole continued feeding long after the initial eruption.
Keck Observatory
Gemini North
VLT in Chile
These hinted at a faint galaxy behind dense dust — but something better was needed.
NASA’s James Webb Space Telescope (JWST) played one of the most crucial roles in the entire investigation.
Webb’s NIRCam cut through dense dust and provided the clearest image of the galaxy ever captured.
The galaxy contains a dark dust lane, and Webb confirmed the GRB shined through that lane.
Webb eliminated the possibility that the burst came from the galaxy’s supermassive black hole.
Webb's NIRSpec measured the galaxy’s distance:
➤ Light from GRB 250702B began its journey 8 billion years ago, before the Sun even existed.
Huei Sears of Rutgers University remarked:
“The resolution of Webb is unbelievable. We can see so clearly that the burst shined through this dust lane spilling across the galaxy.”
This is why Webb is indispensable: no optical telescope on Earth could pierce this much dust.
JWST provided the breakthrough needed to confirm:
the host galaxy
the distance
the burst location
its separation from the central black hole
the galactic structure that shaped the observed light
Record-Setting Energy Output
According to Benjamin Gompertz’s Webb NIRSpec analysis: The burst released the amount of energy a thousand Suns would emit over 10 billion years. This makes GRB 250702B one of the most powerful explosions ever witnessed.
Why This Discovery Matters for Astronomy
GRB 250702B is not just a strange outlier — it is a new blueprint for black hole physics.
Standard GRB models cannot explain such long jet activity.
Either through:
rare intermediate-mass tidal disruptions, or
black hole–helium star mergers
Mergers like this may contribute to the formation of larger black holes over cosmic time.
Only by combining:
Fermi
Swift
Chandra
NuSTAR
Hubble
VLT
Gemini
and James Webb
…were scientists able to reconstruct this cosmic event.
Cutting through Milky Way dust and galaxy-level dust, NIRCam showed the precise burst location.
NIRSpec’s spectroscopy revealed GRB 250702B was 8 billion light-years away.
By showing the burst occurred away from the galactic nucleus, Webb ruled out the possibility that it originated from the supermassive black hole.
This explained why early ground-based detections were faint or unclear.
Its precise imaging allowed researchers to choose between competing black hole scenarios.
In short: Without JWST, this event could not have been correctly interpreted.
GRB 250702B is more than a record-breaker. It is a preview of the kind of cosmic mysteries the James Webb Space Telescope will continue to uncover.
This event:
rewrites GRB models
reveals a new type of stellar destruction
shows black holes feeding for days
proves the importance of multi-scale cosmic monitoring
demonstrates Webb’s unmatched ability to see through dust and distance
As astronomers await future bursts of this type, GRB 250702B stands as one of the most remarkable explosions in the history of observational astronomy — and one of the greatest triumphs for the James Webb Space Telescope.