Forty million years ago, in a nearby galaxy, a star exploded in an unimaginably violent supernova. Forty million years later, on June 29, 2025, the blinding flash from the explosion reached Earth and was detected by the All-Sky Automated Survey for Supernovae, an automated program for detecting supernovae. Although many astronomers immediately turned their attention to this new supernova in an effort to uncover its secrets, a small team of astronomers studied archival data to precisely identify its progenitor star. And he did it!
By carefully aligning images of the galaxy NGC 1637 taken by the Hubble and James Webb space telescopes, this team, led by Charlie Kilpatrick of Northwestern University, was able to identify the progenitor star of the supernova SN 2025pht in images taken in 2024 by the James Webb Space Telescope.
Analysis of the relevant data showed that the star from which the explosion originated appeared surprisingly red. This fact indicates that it was surrounded by large amounts of dust, which has the property of scattering and absorbing the shorter wavelengths of visible radiation corresponding to the color blue. This is perhaps the reddest and “dustiest” red supergiant ever observed exploding as a supernova.
As a general rule, the greater a star’s mass is before it explodes as a supernova, the brighter it is. Therefore, identifying other progenitor stars in images taken before a supernova explosion should be relatively easy. However, that's not exactly the case. One possible explanation is that massive stars nearing the end of their lives are also the “dustiest.” In other words, if they are surrounded by large amounts of dust, their light might even be undetectable. James Webb's observations of SN 2025pht support this hypothesis.
The results of the study were published in the scientific journal AstrophysicalJournalLetters.
Photo: This composite image of the galaxy NGC 1637 was captured by the Hubble and James Webb space telescopes. The four panels on the right side of the image show a close-up of the region of the galaxy where the supernova was detected, before and after its unimaginably violent explosion. The images of the galaxy captured by the James Webb Space Telescope show a red supergiant, which is located in exactly the same position as the bright supernova. This is the first published detection of a hypernova's progenitor star by the James Webb Space Telescope. [Credits: Image: NASA, ESA, CSA, STScI, Charles Kilpatrick (Northwestern), Aswin Suresh (Northwestern); Image Processing: Joseph DePasquale (STScI)].