JWST finds a doomed star just before it explodes. Here's why the discovery’s a huge breakthrough

JWST finds a doomed star just before it explodes. Here's why the discovery’s a huge breakthrough

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The tricky thing about observing the violent, explosive deaths of massive stars – known as supernovae – is that astronomers mostly find them once they've already exploded.

But a team of astronomers using the James Webb Space Telescope have managed to catch a glimpse of a star before and after it exploded.

This has enabled them to identify the supernova's source star at mid-infrared wavelengths for the first time.

Observations are revealing exactly what kind of star it is and where it's been hiding.

This discovery could help solve a long-running mystery as to why massive red supergiant stars seem to rarely explode.

Image showing combined James Webb Space Telescope and Hubble Space Telescope view of spiral galaxy NGC 1637. The star is not visible in the Hubble image before the explosion, but appears in the JWST image. The July 2025 view from Hubble shows the glowing aftermath of the explosion. Credit: NASA, ESA, CSA, STScI, Charles Kilpatrick (Northwestern), Aswin Suresh (Northwestern)
Image showing combined James Webb Space Telescope and Hubble Space Telescope view of spiral galaxy NGC 1637. The star is not visible in the Hubble image before the explosion, but appears in the JWST image. The July 2025 view from Hubble shows the glowing aftermath of the explosion. Credit: NASA, ESA, CSA, STScI, Charles Kilpatrick (Northwestern), Aswin Suresh (Northwestern)

Why it matters – key points

Scientists say that, in theory, red supergiants should make up the majority of so-called 'core collapse' supernovae.

This discovery shows these stars do explode, but are hidden from view within thick clouds of cosmic dust.

However, the James Webb Space Telescope observes the Universe in infrared, which can see through cosmic dust and reveal hidden objects.

Using JWST, the astronomers identified a supernova’s source star – its progenitor – at mid-infrared wavelengths for the first time.

Observations were combined with archive images from the Hubble Space Telescope, showing the explosion did indeed come from a massive red supergiant star.

Image showing combined James Webb Space Telescope and Hubble Space Telescope view of spiral galaxy NGC 1637, and location of supernova SN2025pht. Credit: NASA, ESA, CSA, STScI, Charles Kilpatrick (Northwestern), Aswin Suresh (Northwestern)
Image showing combined James Webb Space Telescope and Hubble Space Telescope view of spiral galaxy NGC 1637, and location of supernova SN2025pht. Credit: NASA, ESA, CSA, STScI, Charles Kilpatrick (Northwestern), Aswin Suresh (Northwestern)

A long wait for a breakthrough

"For multiple decades, we have been trying to determine exactly what the explosions of red supergiant stars look like," Charlie Kilpatrick of Northwestern University, Illinois, USA, 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.

"We’ve been waiting for this to happen – for a supernova to explode in a galaxy that JWST had already observed. We combined Hubble and JWST data sets to completely characterize this star for the first time."

Another massive red supergiant star that's about to go supernova: the famous Betelgeuse in Orion, seen here by the Atacama Large Millimeter/submillimeter Array (ALMA). Credit: ESO
Another massive red supergiant star that's about to go supernova: the famous Betelgeuse in Orion, seen here by the Atacama Large Millimeter/submillimeter Array (ALMA). Credit: ESO

How the discovery was made

The team used the All-Sky Automated Survey of Supernovae to detect the supernova initially on 29 June 2025.

Known as SN2025pht, the supernova is in a galaxy called NGC 1637, 40 million lightyears away from Earth.

They were able to compare Hubble and JWST images of NGC 1637 before and after the star’s explosion.

Doing so, they found SN2025pht’s progenitor star looking very bright and red.

Spiral galaxy NGC 1637 Hubble Space Telescope, 2 December 2024 Credit: ESA/Hubble & NASA, D. Thilker
A previous image of spiral galaxy NGC 1637 captured by the Hubble Space Telescope. Credit: ESA/Hubble & NASA, D. Thilker

This star is about 100,000 times brighter than our Sun, but is hidden behind thick dust, and so it appeared 100 times dimmer in optical light than it would appear without the dust.

Dust also blocked out shorter, bluer wavelengths of light, making it appear very red.

"It’s the reddest, dustiest red supergiant that we’ve seen explode as a supernova," says Aswin Suresh of Northwestern’s Weinberg College of Arts and Sciences, a coauthor on the paper.

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

"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."

Artist's impression of a massive red supergiant going supernova. Credit: Magann / Getty Images
Artist's impression of a massive red supergiant going supernova. Credit: Magann / Getty Images

The problem with dust

More red supergiant progenitors could be hidden from view by thick cosmic dust.

Most massive stars that explode as supernovae are the brightest, most luminous objects in the sky, so they should be easy to spot.

But the most massive aging stars might be the dustiest, astronomers say, and this dust could be dimming their light and making them undetectable.

"I’ve been arguing in favor of that interpretation, but even I didn’t expect to see such an extreme example as SN2025pht," Kilpatrick says.

"It would explain why these more massive supergiants are missing because they tend to be dustier."

A new era for supernova detection?

This is the first time the James Webb Space Telescope has directly identified a supernova progenitor star.

In future, JWST observations should be able to reveal ageing stars across the near- and mid-infrared spectrum, uncovering the most massive hidden stars and providing insight into how they live and die.

The team are continuing the hunt, and say NASA’s upcoming Nancy Grace Roman Space Telescope could help.

"With the launch of JWST and upcoming Roman launch, this is an exciting time to study massive stars and supernova progenitors," Kilpatrick says.

"The quality of data and new findings we will make will exceed anything observed in the past 30 years."

Read the full paper at iopscience.iop.org/article/10.3847/2041-8213/ae04de

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