NASA’s Webb Telescope Locates Former Star That Exploded as Supernova
Forty million years ago, a star in a nearby galaxy exploded, throwing matter across space and generating a brilliant beacon of light. This light traveled through the cosmos and reached Earth on June 29, 2025, where it was detected by the All-Sky Automated Survey for Supernovae. Astronomers immediately turned their resources to this new supernova, designated 2025pht, to learn more. But a team of scientists instead turned to the archives, seeking to use pre-supernova images to identify exactly which star among many had exploded. And they succeeded.
Images of the NGC 1637 galaxy taken by NASA’s James Webb Space Telescope showed a single red supergiant star located exactly where the supernova now shines. This is Webb’s first published detection of a supernova progenitor. The results were published in the Astrophysical Journal Letters.
“We were waiting for this to happen – for a supernova to explode in a galaxy that Webb had previously observed. We combined the Hubble and Webb data sets to fully characterize this star for the first time,” said lead author Charlie Kilpatrick of Northwestern University.
The main image on the left shows a combined Webb and Hubble view of the spiral galaxy NGC 1637. The panels on the right show a detailed view of a red supergiant star before and after its explosion. Before exploding, it is not visible to Hubble, only to Webb. Hubble shows the brilliant consequences.
Image: NASA, ESA, CSA, STScI, Charles Kilpatrick (Northwest), Aswin Suresh (Northwest); Image processing: Joseph DePasquale (STScI)
By carefully aligning Hubble and Webb images taken by NGC 1637, the team was able to identify the progenitor star in images taken by Webb’s MIRI (mid-infrared instrument) and NIRCam (near-infrared camera) in 2024. They found that the star appeared strikingly red – an indication that it was surrounded by dust that blocked shorter, bluer wavelengths of light.
“It’s the reddest, dustiest red supergiant we’ve seen explode as a supernova,” said graduate student and co-author Aswin Suresh of Northwestern University.
This excess dust could help explain a long-standing problem in astronomy that could be described as the case of missing red supergiants. Astronomers expect that the most massive stars that explode as supernovas will also be the brightest and most luminous. They should therefore be easy to identify in pre-supernova images. However, this was not the case.
One possible explanation is that the most massive aging stars are also the dustiest. If they are surrounded by large amounts of dust, their light could be dimmed to the point of becoming undetectable. Webb observations of supernova 2025pht support this hypothesis.
“I argued for this interpretation, but even I didn’t expect to see it as extreme as for supernova 2025pht. That would explain why these more massive supergiants are missing because they tend to be dustier,” Kilpatrick said.
The team was surprised not only by the amount of dust, but also by its composition. Applying computer models to Webb’s observations indicated that the dust is likely rich in carbon, when astronomers might have expected it to be richer in silicate. The team speculates that this carbon could have been extracted from the star’s interior shortly before it exploded.
“Having mid-infrared observations was key to limiting the type of dust we were seeing,” Suresh said.
The team is currently working to search for similar red supergiants that could explode as supernovas in the future. Observations from NASA’s upcoming Nancy Grace Roman Space Telescope could aid this research. Roman will have the resolution, sensitivity and infrared wavelength coverage to not only see these stars, but also potentially witness their variability as they “burp” large amounts of dust near the end of their lives.
The James Webb Space Telescope is the world’s first space science observatory. Webb solves the mysteries of our solar system, looks beyond distant worlds around other stars, and probes 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).
To learn more about Webb, visit:
https://science.nasa.gov/webb
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