Webb Identifies the Exact Star That Exploded 40 Million Years Ago

A flash from the depths of time

A star can shine for millions of years before offering one final surprise. In this particular case, that surprise took the form of a sudden burst of light from a neighboring galaxy. A spectacular event whose origins, however, date back to a time when humanity did not yet exist.

Space is vast, and even light takes time to travel through it. This time lag is the key to the whole story. The star exploded about 40 million years ago, but the light from that explosion did not reach Earth until June 29, 2025. As soon as it arrived, sky-surveillance programs detected it, and astronomers immediately sprang into action to understand the nature of what had just been destroyed.

Supernova 2025pht: A Retrospective Investigation

The event was officially designated Supernova 2025pht after its detection by the All-Sky Automated Survey for Supernovae. Usually, when a star explodes, experts conduct a sort of post-mortem investigation. They work backward, relying on evidence collected after the explosion, such as light curves, spectra, and follow-up images.

But this time, a team of scientists chose a completely different method. Rather than beginning their analysis with the explosion itself, they set out to search for old photographs. Their goal: to find, in telescope archives, the exact star that had been located at the supernova’s site, lost among the countless other stars in its galaxy.

The Composite Image of a Vanished Star

Their persistence paid off. In the archives, the scientists found images of the galaxy NGC 1637 captured by NASA’s James Webb Space Telescope. And within this data, they identified a red supergiant, located precisely where the supernova would later occur. This match is what makes this discovery so significant: it is the first time, in a published study, that the Webb telescope has been used to identify the “parent” star of a supernova before its explosion.

The researchers’ excitement is palpable. “We were waiting for this to happen—for a supernova to explode in a galaxy that Webb had already observed. We combined the Hubble and Webb datasets to fully characterize this star for the first time,” explains Charlie Kilpatrick of Northwestern University, the study’s lead author. To confirm the identification, the team meticulously aligned images from both telescopes, focusing on Webb’s 2024 observations taken with its MIRI and NIRCam instruments.

The Mystery of the Red Dust

What they saw was strange. The star appeared abnormally red, a phenomenon that often occurs when cosmic dust blocks shorter wavelengths of light, such as blue. “This is the reddest and dustiest red supergiant we’ve ever seen explode as a supernova,” says Aswin Suresh, a graduate student at Northwestern and co-author of the study. This dust is crucial because it could solve an old astronomical puzzle, sometimes called the problem of the “missing” red supergiants.

Astronomers expect the most massive stars that explode as supernovae to be bright enough to be spotted in old images. Yet many of them appear to be missing. One of the leading theories suggests that the largest and oldest stars might be enveloped in a dust cocoon so thick that it obscures them, making them very difficult to detect. This star fits that profile perfectly.

“I supported this interpretation, but even I didn’t expect to see it to such an extreme degree as with Supernova 2025pht. This would explain why these more massive supergiants are missing, since they tend to be dustier,” adds Charlie Kilpatrick.

Toward a New Understanding of Stellar Giants

The team also took a close look at the composition of this dust. Using computer models fed by Webb data, they discovered clues suggesting that the dust is likely carbon-rich. This comes as a surprise, as astronomers expected to find dust richer in silicates around a red supergiant. The researchers believe this carbon may have been transported up from the star’s depths shortly before its explosion.

“Having observations in the mid-infrared was essential for determining the type of dust we were seeing,” explains Aswin Suresh. The team is now searching for other similar red supergiants. The goal is to identify them before they explode to better understand how massive stars lose material at the end of their lives.

NASA’s future Nancy Grace Roman Space Telescope could play a major role in this quest. It should be able to detect these stars in infrared light and track changes as they “spew” large amounts of dust. The full study was published in the scientific journal Astrophysical Journal Letters.

Source: earth.com

Webb Identifies the Exact Star That Exploded 40 Million Years Ago