Updated on: December 08, 2025 | By: Jameswebb Discovery Editorial Team

James Webb Telescope Unveils GRB 250702B — The Longest Gamma-Ray Burst Ever as a Black Hole Devours a Star

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.

Introduction: A Record-Breaking Blast That Shattered Expectations

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.

What Made GRB 250702B So Exceptional?

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:

1. The Collapse of a Massive Star

Usually lasts seconds to minutes.

2. The Merger of Two Neutron Stars

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.

A Black Hole Consuming a Star: The Leading Explanation

Astronomers now agree the most probable cause was a black hole eating a star — but there are two competing models.

Scenario 1: An Intermediate-Mass Black Hole Tears Apart a Passing Star

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.

Scenario 2: A Stellar-Mass Black Hole Merges With Its Companion Star

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.

How NASA’s Missions Worked Together to Decode the Explosion

No single instrument could fully observe the burst. Instead, NASA’s space fleet formed a coordinated network across multiple wavelengths:

Gamma-Ray Observations

• 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.

X-Ray Follow-Up

• 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.

Ground-Based Optical & Infrared

• Keck Observatory
  
  

• Gemini North
  
  

• VLT in Chile
  
  

These hinted at a faint galaxy behind dense dust — but something better was needed.

The James Webb Space Telescope Reveals the Host Galaxy in Unprecedented Detail

NASA’s James Webb Space Telescope (JWST) played one of the most crucial roles in the entire investigation.

What Webb Saw

• 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.

It challenges how we think stars die.

Standard GRB models cannot explain such long jet activity.

It reveals new ways black holes consume stars.

Either through:

• rare intermediate-mass tidal disruptions, or
  
  

• black hole–helium star mergers
  
  

It expands our understanding of black hole growth.

Mergers like this may contribute to the formation of larger black holes over cosmic time.

It highlights the power of multi-mission astronomy.

Only by combining:

• Fermi

• Swift

• Chandra

• NuSTAR

• Hubble

• VLT

• Gemini

• and James Webb
  
  

…were scientists able to reconstruct this cosmic event.

How the James Webb Telescope Was Essential to Solving This Mystery

1. Webb Provided the Clearest Image of the Host Galaxy

Cutting through Milky Way dust and galaxy-level dust, NIRCam showed the precise burst location.

2. Webb Measured the Galaxy’s Distance

NIRSpec’s spectroscopy revealed GRB 250702B was 8 billion light-years away.

3. Webb Helped Eliminate Incorrect Models

By showing the burst occurred away from the galactic nucleus, Webb ruled out the possibility that it originated from the supermassive black hole.

4. Webb Confirmed the Peculiar Dust Lane Structure

This explained why early ground-based detections were faint or unclear.

5. Webb Guided Theoretical Models

Its precise imaging allowed researchers to choose between competing black hole scenarios.

In short: Without JWST, this event could not have been correctly interpreted.

Conclusion: GRB 250702B Opens a New Chapter in Black Hole Astronomy

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.