Free Astronomy Magazine May-June 2026

35 MAY-JUNE 2026 ASTRO PUBLISHING The results were published in the As- trophysical Journal Letters . “We’ve been waiting for this to hap- pen – for a supernova to explode in a galaxy that Webb had already ob- served. We combined Hubble and Webb data sets to completely char- acterize this star for the first time,” said lead author Charlie Kilpatrick of Northwestern University. By carefully aligning Hubble and Webb images taken of NGC 1637, the team was able to identify the progenitor star in images taken by Webb’s MIRI (Mid-Infrared Instru- ment) and NIRCam (Near-Infrared Camera) in 2024. They found that the star appeared surprisingly red – an indication that it was surrounded by dust that blocked shorter, bluer wavelengths of light. “It’s the reddest, most dusty red su- pergiant that we’ve seen explode as a supernova,” said graduate student and co-author Aswin Suresh of Northwestern University. This excess of dust could help ex- plain a long-standing problem in as- tronomy that could be described as the case of the missing red super- giants. Astronomers expect the most massive stars that explode as super- novas to also be the brightest and most luminous. So, they should be easy to identify in pre-supernova im- ages. However, that hasn’t been the case. One potential explanation is that the most massive aging stars are also the dustiest. If they’re surrounded by large quantities of dust, their light could be dimmed to the point of undetectability. The Webb obser- vations of supernova 2025pht sup- port that hypothesis. “I’ve been arguing in favor of that interpretation, but even I didn’t ex- pect 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,” said Kilpatrick. The team was not only surprised by the amount of dust, but also by its composition. Applying computer models to the Webb observations indicated that the dust is likely car- bon-rich, when astronomers would have expected it to be more silicate- rich. The team speculates that this carbon might have been dredged up from the star’s interior shortly be- fore it exploded. “Having observations in the mid-in- frared was key to constraining what kind of dust we were seeing,” said Suresh. The team now is working to look for similar red supergiants that may ex- plode as supernovas in the future. Observations by NASA’s upcoming Nancy Grace Roman Space Telescope may help this search. Roman will have the resolution, sensitivity, and infrared wavelength coverage to not only see these stars, but also po- tentially witness their variability as they “burp” out large quantities of dust near the end of their lives. P revious page: The main image at left shows a combined Webb and Hubble view of spiral galaxy NGC 1637. Panels at right show a detailed view of a red supergiant star before and after it exploded. Before explod- ing, it is not visible to Hubble, only to Webb. Hubble shows the glowing aftermath. [NASA, ESA, CSA, STScI, Charles Kilpatrick (Northwestern), Aswin Suresh (Northwestern); Image Processing: Joseph DePasquale (STScI)] T wo of the 14-centimeter diameter telescopes in use for the All Sky Automat- ed Survey for SuperNovae (ASAS-SN), an Ohio State-led automated tele- scope network that observes the entire sky every night. ASAS-SN consists of 20 automated telescopes distributed around the world that combine to compile thousands of images per night to find things up to 50,000 times fainter than the human eye can see. [Wayne Rosing] supernova, designated 2025pht, to learn more about it. But one team of scientists instead turned to archives, seeking to use pre-supernova im- ages to identify exactly which star among many had exploded. And they succeeded. Images of galaxy NGC 1637 taken by NASA’s James Webb Space Telescope showed a single red supergiant star located exactly where the supernova now shines. This represents the first published detection of a supernova progenitor by Webb. !