JWST Unveils Dust-Obscured Red Supergiant Prior to Supernova Explosion

Astronomers have long sought to understand the apparent scarcity of red supergiant stars observed before they undergo supernova explosions. Recent observations using the James Webb Space Telescope (JWST) have provided new insights into this phenomenon.

In a study published on October 8 in The Astrophysical Journal Letters, researchers detailed their identification of a red supergiant star, heavily obscured by dust, shortly before it exploded as a supernova. This marks the first time JWST has detected a progenitor star in such detail prior to its explosion.

The supernova, designated SN 2025pht, was detected on June 29 in a galaxy approximately 40 million light-years from Earth. Both JWST and the Hubble Space Telescope had previously imaged this region, with Hubble's observations dating back to 1994 and JWST's in 2024. By comparing these pre-explosion datasets, the team pinpointed the specific star that later detonated.

"We've been waiting for this to happen — for a supernova to explode in a galaxy that JWST had already observed," said Charlie Kilpatrick of Northwestern University, who led the study. "Only now, with JWST, do we finally have the quality of data and infrared observations that allow us to say precisely the exact type of red supergiant that exploded and what its immediate environment looked like."

The progenitor star was found to be extraordinarily bright and incredibly red, indicating it was enveloped by a dense cocoon of dust. Although it shone about 100,000 times brighter than our sun, its visible light was dimmed by more than 100 times due to the surrounding dust.

"It's the reddest, dustiest red supergiant that we've seen explode as a supernova," noted study co-author Aswin Suresh, a graduate student in physics and astronomy at Northwestern.

These findings suggest that many red supergiant stars do indeed explode as supernovae but are often hidden behind thick layers of dust, rendering them invisible to optical telescopes. This discovery helps explain the previously observed scarcity of such stars prior to their explosions.

"That tells us that previous explosions might have been much more luminous than we thought because we didn't have the same quality of infrared data that JWST can now provide," Kilpatrick added.

The study also revealed that the dust surrounding the progenitor star was unusually rich in carbon, rather than the silicate-based dust typically seen in red supergiants. This may indicate that powerful convection deep inside the star dredged up carbon from its core during its final years, altering its chemistry just before it exploded.

This discovery opens a new window into the life cycles of massive stars. With JWST and the upcoming Nancy Grace Roman Space Telescope, astronomers will be able to track more of these hidden giants in their final moments.

"With the launch of JWST and upcoming Roman launch, this is an exciting time to study massive stars and supernova progenitors," Kilpatrick said. "The quality of data and new findings we will make will exceed anything observed in the past 30 years."