Франц-Хятадын хамтарсан SVOM хиймэл дагуул эртний орчлон ертөнцийн нууцыг тайлах гамма туяаны тэсрэлтүүдийг илрүүлэв

Eight gamma-ray bursts detected by the French-Chinese SVOM satellite are puzzling astronomers. Each one produced an X-ray afterglow, yet when SVOM’s visible-light telescope looked at the same location, it found nothing. The mission team says these unexplained bursts may have come from the universe’s first billion years.

By June 22, 2026, SVOM had spent two years in orbit and recorded 318 gamma-ray bursts. Most are brief flashes of high-energy light produced by some of the most violent explosions known. But these eight stand out because their afterglows seem to disappear exactly where astronomers would normally expect to find visible light.

That missing signal does not prove that the bursts are extraordinarily distant. None of the eight has a redshift measurement precise enough to establish where it came from. For now, they remain high-redshift candidates, and their true nature is still uncertain.

Why Would a Gamma-Ray Burst Disappear?

The explanation may lie in what happens to light as it crosses the universe. At extreme distances, neutral hydrogen between galaxies absorbs much of the ultraviolet and visible light coming from an afterglow. At the same time, cosmic expansion stretches the surviving radiation toward longer wavelengths.

This means an explosion can effectively vanish from visible-light observations while remaining detectable in the near-infrared. That pattern is one of the clues astronomers use when searching for objects from the early universe. An X-ray afterglow with no optical counterpart can therefore be a reason to investigate whether the source lies at very high redshift.

But there are other reasons a burst can appear optically dark, so astronomers need more than a missing visible signal. A secure distance usually requires spectroscopy or another strong redshift measurement. Until that happens, the eight SVOM bursts remain intriguing possibilities rather than confirmed explosions from the first billion years.

One Earlier Burst Showed What Confirmation Looks Like

There is already one SVOM event that demonstrates what can happen when astronomers catch the afterglow quickly enough. GRB 250314A reached the satellite on March 14, 2025, and lasted about 10 seconds. Bursts lasting longer than a couple of seconds are usually associated with the collapse of a massive star.

In such an event, the star’s core collapses and can launch narrow jets of material moving at nearly the speed of light. If one of those jets points toward Earth, the burst and its afterglow can remain visible across enormous cosmic distances. The problem is that the afterglow fades quickly, so follow-up observations have to begin fast.

NASA’s Swift observatory and the Chinese-European Einstein Probe located the X-ray source, while the Nordic Optical Telescope detected the afterglow in near-infrared light. The European Southern Observatory’s Very Large Telescope then obtained spectra that placed the burst at redshift 7.3. That means the explosion happened when the universe was only about 5 percent of its current age.

According to the SVOM team, GRB 250314A is the third most distant gamma-ray burst ever confirmed through spectroscopy. The SVOM detection paper in Astronomy & Astrophysics lists only two confirmed bursts at greater redshift, GRB 090423A at 8.23 and GRB 120923A at 7.8.

Redshift Changed Both the Light and the Timing

Redshift measures how much the universe expanded while light was traveling toward Earth. As the universe expands, that light is stretched toward redder and eventually infrared wavelengths. At a redshift of 7.3, this effect is strong enough that near-infrared astronomy becomes essential for studying the explosion.

Cosmic expansion also stretches time from our perspective. A nearby supernova may brighten over a few weeks, but an extremely distant one can appear to evolve over months. That is why a team led by Andrew Levan of Radboud University waited about three and a half months before observing the source with the James Webb Space Telescope.

The team used a fast-track observing program designed for events that require telescope time on short notice. Their timing was intended to catch the supernova close to its expected peak brightness. Webb then provided the confirmation astronomers had been waiting for.

Webb Found the Earliest Supernova Ever Detected

The telescope detected the fading explosion as a faint red point and also observed the galaxy that hosted the star. The result identified the earliest supernova ever detected, from a star that exploded when the universe was about 730 million years old. The previous record holder came from a time when the universe was roughly 1.8 billion years old.

The supernova was remarkable not only because of its age, but because it looked unexpectedly familiar. “Almost every supernova ever studied has been relatively nearby to us,” said Antonio Martin-Carrillo of University College Dublin. Yet the explosion did not appear radically different from examples seen much closer to Earth.

“Webb showed that this supernova looks exactly like modern supernovae,” said Nial Tanvir of the University of Leicester. Researchers still need more observations to search for subtler differences and to understand why a stellar explosion from such an early period of cosmic history appears so similar to modern ones.

Confirming the Next One Could Come Down to Hours

The challenge now is repeating that success. A SVOM team overview posted in July 2026 notes that the Very Large Telescope obtained spectra of GRB 250314A about 17 hours after the burst. That was fast enough to determine its redshift, but future events may require even quicker follow-up.

The team points to better infrared follow-up as one of the keys. The CAGIRE near-infrared camera is scheduled for installation on the Colibrí telescope at the end of 2026, adding to a limited network of instruments capable of reacting quickly to distant bursts. Faster observations increase the chance of measuring an afterglow before it fades beyond reach.

Even with better tools, these events are expected to remain rare. A 2025 modeling study from Purple Mountain Observatory estimated that SVOM’s main detector might catch about 0.7 bursts per year beyond redshift 6, while Einstein Probe’s wide-field X-ray telescope might detect about five.

By June 12, 2026, SVOM’s ECLAIRs telescope had pinpointed 107 bursts, and 40 had measured redshifts. GRB 250314A remains the only one securely confirmed to come from the universe’s first billion years. The other eight are still mysteries, but one of them could eventually become the next confirmed glimpse of a star dying more than 13 billion years ago.

Enjoyed this article? Subscribe to our free newsletter for engaging stories, exclusive content, and the latest news.