NASA's James Webb Space Telescope has located a former star that exploded 40 million years ago as a supernova in a nearby galaxy. The light from the explosion did not reach Earth till June 29, 2025, when the All-Sky Automated Survey for Supernovae detected it. Using data, scientists have managed to piece together images of galaxy NGC 1637, where the explosion exactly happened.
Data from the Webb and Hubble telescopes show a single red supergiant star located exactly where the supernova, designated 2025pht, currently exists. The results, published in the Astrophysical Journal Letters, represent the first published detection of a supernova progenitor by Webb.
“What if you could go back in time and see a star just before it goes supernova? Archives of telescope data are essentially letting astronomers do just that,” the Webb telescope shared in its thread on X.
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NASA's New Discovery
The scientists carefully aligned images of NGC 1637 taken by Hubble and Webb to identify the progenitor star in photos snapped by Webb's NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument) in 2024. Researchers discovered that the star appeared red, indicating that the dust surrounding it blocked shorter, bluer wavelengths of light.
“It's the reddest, most dusty red supergiant that we've seen explode as a supernova,” graduate student and co-author Aswin Suresh of Northwestern University said, as per a page on NASA.
This excess of dust might help explain the case of the missing red supergiants, a long-standing problem in astronomy. Astronomers expect that the biggest stars that explode as supernovas will also be the brightest and most luminous and should be easy to identify in pre-supernova images. However, that is not the case.
A potential explanation for this is that the most massive aging stars have the most dust as well. This can dim their light to the point of undetectability. The Webb observations of supernova 2025pht support this hypothesis.
The lead author of the study, Charlie Kilpatrick of Northwestern University, told NASA, “I've been arguing in favor of that interpretation, but even I didn't expect to see it as extreme as it was for supernova 2025pht. It would explain why these more massive supergiants are missing because they tend to be more dusty.”
What Discovery Can Reveal About Carbon Burps
The composition of the dust also threw up surprises. While scientists expected it to be more silicate-rich, it is more likely to be carbon-rich. The research team believes that the carbon may have been dredged up from the star's interior shortly before the explosion.
“Having observations in the mid-infrared was key to constraining what kind of dust we were seeing,” said Suresh.
What's Next For The Researchers?
The team is currently working to look for similar red supergiants that could explode as supernovas in the future. Observations by NASA's upcoming Nancy Grace Roman Space Telescope are expected to help the search. The telescope will have the sensitivity, resolution, and infrared wavelength coverage to see these stars. It can also potentially witness their variability as the stars “burp” out large amounts of dust close to the end of their lives.
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