Webb glimpses doomed star before its explosion

The article below is taken from a release by Northwestern University on October 8, 2025. Edits by EarthSky.

Will this doomed star solve a decades-old mystery?

Scientists at Northwestern University said on October 8, 2025, that they’ve captured the most detailed glimpse yet of a doomed star before it exploded. And, they said, this star is the dustiest and reddest supernova progenitor – or source star – yet observed.

Astronomers detected the supernova, dubbed SN2025pht, on June 29, 2025. The Northwestern research team then studied earlier James Webb Space Telescope imagery of the galaxy in which the supernova was spotted to identify the progenitor star. They said:

These observations – combined with archival images from the Hubble Space Telescope – revealed the explosion came from a massive red supergiant star, cloaked in an unexpected shroud of dust.

This marks the first time a supernova’s source star has been identified at mid-infrared wavelengths.

The researchers said the discovery might help solve the decades-old mystery of why massive red supergiants are rarely seen to explode. That’s surprising, because scientists’ models predict these kinds of stars should make up the majority of core-collapse supernovae. That’s when massive stars, typically over eight times more massive than our sun, explode because their iron cores can no longer hold out against the force of gravity.

The new study suggests these stars do explode, but are simply hidden out of sight within thick clouds of dust. With Webb’s new capabilities, astronomers can finally pierce through the dust to spot these phenomena, closing the gap between theory and observation.

The peer-reviewed study was published on October 8, 2025, in The Astrophysical Journal Letters.

Meet researchers Charlie Kilpatrick and Aswin Suresh

Northwestern’s Charlie Kilpatrick led the study. He explained:

For multiple decades, we have been trying to determine exactly what the explosions of red supergiant stars look like. Only now, with [the Webb Space Telescope], 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.

We’ve been waiting for this to happen, for a supernova to explode in a galaxy that Webb had already observed.

We combined Hubble and Webb data sets to completely characterize this star for the first time.

Kilpatrick is an expert on the lives and deaths of massive stars. He’s a research assistant professor at Northwestern’s Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA).

Another key coauthor on the paper is Aswin Suresh. He is a graduate student in physics and astronomy at Northwestern’s Weinberg College of Arts and Sciences and member of Kilpatrick’s research group.

Reddest, dustiest progenitor ever observed

The astronomers first detected the supernova on June 29, 2025, using the All-Sky Automated Survey of Supernovae. They dubbed it SN2025pht. Its light had traveled from a nearby galaxy called NGC 1637, located 40 million light-years away from Earth.

By comparing Hubble and Webb images of the galaxy NGC 1637 – from before and after the star’s explosion – Kilpatrick, Suresh and their collaborators found SN2025pht’s progenitor star. It was immediately striking because it was extremely bright and incredibly red. The star shined about 100,000 times more brightly than our sun. But a surrounding dust obscured much of this light. The dusty veil was so thick, in fact, that the star appeared more than 100 times dimmer in visible light than it would appear without the dust.

Because dust blocked out shorter, bluer wavelengths of light, the star also appeared surprisingly red. Suresh commented:

It’s the reddest, dustiest red supergiant that we’ve seen explode as a supernova.

Massive stars in the late stages of their lives, red supergiants are among the largest stars in the universe. When their cores collapse, they explode as Type II supernovae, leaving behind either a neutron star or a black hole.

The most familiar example of a red supergiant is Betelguese. It is the bright reddish star in the shoulder of the constellation Orion.

Kilpatrick added

SN2025pht is surprising because it appeared much redder than almost any other red supergiant we’ve seen explode as a supernova. 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.

Clues hidden in dust

The deluge of dust could help explain why astronomers have struggled to find red supergiant progenitors. Indeed, most massive stars that explode as supernovae are the brightest and most luminous objects in the sky. So, theoretically, they should be easy to spot before they explode. But that hasn’t been the case.

In addition, astronomers posit that the most massive aging stars also might be the dustiest. These thick cloaks of dust might dim the stars’ light to the point of utter undetectability. And now, the new Webb observations support this hypothesis. Kilpatrick said:

I’ve been arguing in favor of that interpretation, but even I didn’t expect to see such an extreme example as SN2025pht. It would explain why these more massive supergiants are missing because they tend to be dustier.

In addition to the presence of dust itself, the dust’s composition was also surprising. While red supergiants tend to produce oxygen-rich, silicate dust, this star’s dust appeared rich with carbon. This suggests that powerful convection in the star’s final years may have dredged up carbon from deep inside, enriching its surface and altering the type of dust it produced. Kilpatrick added:

The infrared wavelengths of our observations overlap with an important silicate dust feature that’s characteristic of some red supergiant spectra. This tells us that the wind was very rich in carbon and less rich in oxygen, which also was somewhat surprising for a red supergiant of this mass.

A new era for exploding stars?

The new study marks the first time astronomers have used the Webb telescope to directly identify a supernova progenitor star. And they say this fact opens the door to many more discoveries. By capturing light across the near- and mid-infrared spectrum, they said, the Webb can reveal hidden stars and provide missing pieces for how the most massive stars live and die.

Now, the team said they’re searching for similar red supergiants that may explode as supernovae in the future. Observations by NASA’s upcoming Nancy Grace Roman Space Telescope might help this search. Roman will have the resolution, sensitivity and infrared wavelength coverage to see these stars and potentially witness their variability as they expel out large quantities of dust near the end of their lives. Kilpatrick said:

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

Bottom line: For decades, astronomers have wanted to know exactly what the explosion of a doomed star – a red supergiant due to go supernova – looks like. The Webb Space Telescope has made that knowledge possible.

Source: The Type II SN 2025pht in NGC 1637: A Red Supergiant with Carbon-rich Circumstellar Dust as the First JWST Detection of a Supernova Progenitor Star

Via Northwestern Now

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