Webb Telescope Spots Earliest Supernova – 730 Million Years After Big Bang

The James Webb Space Telescope has detected a supernova that exploded when the universe was just 730 million years old, marking the earliest observation of its kind to date. The telescope’s sharp near-infrared imaging also allowed astronomers to pinpoint the faint host galaxy of the supernova. This rapid observation, made on July 1, supported an international team of telescopes that initially detected a powerful flash of light – a gamma-ray burst – in mid-March.

This discovery breaks Webb’s own previous record; the previously earliest supernova observed occurred when the universe was 1.8 billion years old. “Only Webb could directly demonstrate that this light came from a supernova, a collapsing massive star,” said Andrew Levan, lead author of one of two new papers published in Astronomy & Astrophysics Letters and a professor at Radboud University in Nijmegen and the University of Warwick in the United Kingdom. “This observation also shows that we can use Webb to find individual stars at a time when the universe was only 5% of its current age.” While a gamma-ray burst typically lasts seconds to minutes, a supernova usually brightens rapidly over weeks before slowly fading. This supernova, however, continued to brighten for months. Because it exploded so early in the universe’s history, its light has been stretched as the universe expanded over billions of years, lengthening the time it takes for events to unfold.

The Webb observations were intentionally scheduled three and a half months after the gamma-ray burst ended, anticipating that the underlying supernova would be at its brightest at that time. “Webb provided the rapid and sensitive follow-up we needed,” said Benjamin Schneider, a co-author and postdoctoral researcher at the Laboratoire d’Astrophysique de Marseille in France. Gamma-ray bursts are exceptionally rare events. Short-duration bursts, lasting just a few seconds, are thought to be caused by the collision of two neutron stars or a neutron star and a black hole. Longer bursts, like the one observed lasting approximately 10 seconds, are often associated with the explosive death of massive stars. The ability to study these early stellar events provides crucial insights into the conditions and processes that shaped the early universe.

Immediate, Rapid Follow-up to the Source

The initial alert came on March 14. News of the gamma-ray burst from a very distant source originated from the SVOM mission (Space-based multi-band astronomical Variable Objects Monitor), a French-Chinese telescope launched in 2024 designed to detect transient events. Within an hour and a half, NASA’s Neil Gehrels Swift Observatory located the X-ray source of the burst in the sky, enabling further observations to determine the distance for Webb. Eleven hours later, the Nordic Optical Telescope in the Canary Islands detected a faint afterglow of infrared light from the gamma-ray burst, suggesting the burst might be linked to a very distant object. Four hours after that, the European Southern Observatory’s Very Large Telescope in Chile estimated the object existed 730 million years after the Big Bang. “There have only been a handful of gamma-ray bursts detected in the first billion years of the universe in the last 50 years,” Levan stated. “This particular event is very rare and very exciting.”

Striking Similarity to Nearby Supernovae

As the earliest and most distant supernova observed to date, researchers compared it to what they know well: modern, nearby supernovae. Surprisingly, the two proved remarkably similar. Why? Relatively little is known about the first billion years of the universe. Early stars likely contained fewer heavy elements, were more massive, and had shorter lifespans, and existed during the epoch of reionization, when gas between galaxies was largely opaque to high-energy light. “We went in with an open mind,” said Nial Tanvir, a co-author and professor at the University of Leicester in the United Kingdom. “And lo and behold, Webb showed that this supernova looks just like modern supernovae.” More data is needed to identify subtle differences before researchers can determine why such an early supernova resembles those closer to home.

First Look at the Supernova’s Host Galaxy

“The Webb observations suggest that this distant galaxy is similar to other galaxies that existed in the same period,” said Emeric Le Floc’h, a co-author and astronomer at CEA Paris-Saclay (Commissariat à l’Énergie Atomique et aux Énergies Alternatives) in France. Limited information can be gleaned from the galaxy’s light, which is smeared into just a few pixels, making it appear as a red smudge. The fact that it can be seen at all is a breakthrough. The research team has already planned to redeploy Webb in international follow-up investigations of gamma-ray bursts from objects in the early universe. The team has been granted time to observe events with Webb and now has a new goal: to learn more about galaxies in the distant universe by capturing the afterglow of gamma-ray bursts. “That glow will help Webb see more and give us a ‘fingerprint’ of the galaxy,” Levan explained. The research team observed supernova GRB 250314A with a rapid Director’s Discretionary Time program.

The James Webb Space Telescope is the world’s premier observatory for space science. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).

Source: NASA