Early Universe Supernova GRB 250314A | James Webb Space Telescope
On the left, the characteristic jets of a gamma-ray burst can be seen punching through material that was ejected by the supernova explosion.
On the right, the glowing supernova shines through gas continuing to rush outward from the blast.
In the background, the supernova’s host galaxy contains numerous bright star-forming regions.
With this observation, Webb also broke its own record: The previous chart-topping supernova existed when the Universe was 1.8 billion years old.
“Only Webb could directly show that this light is from a supernova—a collapsing massive star,” said Andrew Levan, the lead author of one of two new papers in Astronomy and Astrophysics Letters and a professor at Radboud University in Nijmegen, Netherlands, and the University of Warwick in the United Kingdom. “This observation also demonstrates that we can use Webb to find individual stars when the Universe was only 5% of its current age.”
While a gamma-ray burst typically lasts for seconds to minutes, a supernova rapidly brightens over several weeks before it slowly dims. In contrast, this supernova brightened over months. Since it exploded so early in the history of the Universe, its light was stretched as the cosmos expanded over billions of years. As light is stretched, so is the time it takes for events to unfold. Webb’s observations were intentionally taken three and a half months after the gamma-ray burst ended, since the underlying supernova was expected to be brightest at that time.
“Webb provided the rapid and sensitive follow-up we needed,” said Benjamin Schneider, a co-author and a postdoctoral researcher at the Laboratoire d'Astrophysique de Marseille in France.
Gamma-ray bursts are incredibly rare. Those that last a few seconds may be caused by two neutron stars, or a neutron star and a black hole colliding. Longer bursts like this one, lasting around 10 seconds, are frequently linked to the explosive deaths of massive stars.
Immediate, nimble investigation of the source
The first alert chimed on March 14, 2025. The news of the gamma-ray burst from a very distant source came from the Space-based multi-band astronomical Variable Objects Monitor (SVOM) mission, a Franco-Chinese telescope that launched in 2024 and was designed to detect fleeting events.
Within an hour and a half, NASA’s Neil Gehrels Swift Observatory pinpointed the X-ray source’s location on the sky. That enabled subsequent observations that would pin down the distance for Webb. Eleven hours later, the Nordic Optical Telescope on the Canary Islands in Spain was queued up and revealed an infrared-light gamma-ray burst afterglow, an indication that the gamma ray might be associated with a very distant object. Four hours later, the European Southern Observatory’s Very Large Telescope in Chile estimated the object existed 730 million years after the big bang.
“There are only a handful of gamma-ray bursts in the last 50 years that have been detected in the first billion years of the Universe,” Levan said. “This particular event is very rare and very exciting.”
Shockingly similar to nearby supernovae
Since this is the earliest, farthest supernova to be detected to date, researchers compared it to what they know in great detail—modern, nearby supernovae. The two turned out to be very similar, which surprised them.
Why? Little is still known about the first billion years of the Universe. Early stars likely contained fewer heavy elements, were more massive, and led shorter lives. They also existed during the Era of Reionisation, when gas between galaxies was largely opaque to high-energy light.
“We went in with open minds,” said Nial Tanvir, a co-author and a professor at the University of Leicester in the United Kingdom. “And lo and behold, Webb showed that this supernova looks exactly like modern supernovae.” Before researchers can determine why such an early supernova is similar to nearby supernovae, more data is needed to pinpoint tiny differences.
First look at supernova’s host galaxy
“Webb’s observations indicate that this distant galaxy is similar to other galaxies that existed at the same time,” said Emeric Le Floc’h, a co-author and astronomer at the CEA Paris-Saclay (Commissariat à l'Énergie Atomique et aux Énergies Alternatives) in France. Since the galaxy’s light is blended into a few pixels, making the galaxy look like a reddened smudge, what we can learn about it is still limited. Seeing it at all is a breakthrough.
The researchers have already laid plans to reenlist Webb in the international effort to learn more about gamma-ray bursts emitted by objects in the early Universe. The team has been approved to observe events with Webb and now have a new aim: to learn more about galaxies in the distant Universe by capturing the afterglow of the gamma-ray bursts themselves. “That glow will help Webb see more and give us a ‘fingerprint’ of the galaxy,” Levan said.
Release Date: Dec. 9, 2025
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