The mystery of the universe's missing exploding stars
According to scientists, red supergiant stars should produce more supernovas. But astronomers just aren’t spotting them. Here's how they plan to crack the case.
In recent years, whenever astronomers have gazed into the night sky, they’ve noticed something peculiar: Some of its massive stars—the true titans of the cosmos—appear to be missing.
Stars that are at least eight times the mass of our own Sun are thought to end their lives as gargantuan explosions called supernovae. Since 1987, scientists have caught around 30 stars in the act of exploding as core-collapse supernovae, which is when a star runs out of nuclear fuel, causing it to implode then cataclysmically explode. Most of these stars were red supergiants, very bright, crimson-hued stellar furnaces.
The largest of these—stars 18 times the mass of the sun, or bigger—are extremely bright and should be easy to spot before they go boom. But around a decade ago astronomers realized that they weren’t seeing as many of these colossal self-destructing stars as they’d expect—and no one knows why. Now, one Earth’s most powerful space telescopes may finally solve this mystery.
The red supergiant puzzle has two possible solutions. The first is that “they’re not exploding at all,” says Charlie Kilpatrick, an astronomer at Northwestern University in Illinois. Instead, upon dying, these supergiants are vanishing from view as they transform immediately into a black hole. The second possibility is that as they approach death, some red supergiants cough out a maelstrom of dust. Both scenarios would obscure the stars from the views of most telescopes.
Fortunately, the James Webb Space Telescope has confidently entered the chat. This $10-billion space observatory sees in infrared light, which means it can spot evidence of stars suddenly disappearing into black holes and peer through any thick dusty coats camouflaging supergiants. Already, Webb is finding evidence that may tip the scales in favor of one solution.
(See the oldest and farthest supernovae.)
The veiled supergiants
If these titanic red supergiants are concealed by their own dusty blankets, this would hide some from view. Telescopes could pick up other smaller supergiants, but the dust would dim their light; that means astronomers would underestimate their brightness and their mass, ultimately classifying them as smaller stars.
Finding clear evidence to support this idea, though, has been troublesome. Fortunately, in 2025, astronomers got lucky. That summer, 40 million light-years away in the constellation Eridanus, a star exploded. All-Sky Automated Survey for Supernovae, or ASASSN, global telescopic network caught the outburst, within the galaxy NGC 1637.
This supernova, designated 2025pht, set supergiant seekers abuzz. Astronomers wondered if they could use archival images of that galaxy to find the star that blew up. The Hubble Space Telescope, which sees in visible light, came up empty. “Any dust makes it impossible for the light to escape,” says Aswin Suresh, a graduate student at Northwestern University, and an author of a recent paper that examined 2025pht.
Webb, however, came in clutch. “We could find the star that exploded,” says Kilpatrick, another of the study’s authors. It was an exceedingly dusty red supergiant. This bolsters the theory that a lot of the missing red supergiants, he says, “are hidden by dust.”
(Here’s a behind-the-scenes look at how the James Webb telescope was built.)
The failed supernovae
It’s still possible, though, that other red supergiants are simply “blinking out of existence,” says Emma Beasor, an astronomer at Liverpool John Moores University in England.
When a dying star is unable to shed its outer layers in a giant explosion, “gravity instantly wins, and it’s able to pull back everything into the core of the star, which leads to the formation of a black hole,” says Kishalay De, an astronomer at Columbia University. If these so-called ‘failed supernovae’ are real, they would be extremely difficult to spot with telescopes—and the red supergiants that existed beforehand would simply implode out of existence.
The notion of failed supernovae has “gained popularity over the years,” says De. But only candidates for them have been found so far—nothing definitive.
“We still don’t really know what they should look like, what to expect from them,” says Beasor. Some suspect dying supergiant stars do instantly disappear and become black holes. Others think you’d get a tiny burst of light first, which then fizzles away completely. “The theory is still a bit wobbly.”
In February, a study by De and his team revealed a new failed supernova candidate detected in archival images taken by NEOWISE, a now-defunct infrared space observatory designed to spot near-Earth asteroids and comets. They watched a source of light in the nearby Andromeda Galaxy brighten a modest amount in the mid-2010s before rapidly dimming.
“It went from being this superbright star to basically being nothing there at all,” says De. “It faded into darkness.” They reckon that this was a supergiant star that turned into a black hole. In this case, it was probably a yellow supergiant, “very much like a red supergiant,” says De, but slightly hotter. (Red supergiants can turn yellow in their elderly years.)
If this is truly a failed supernova, then it would mean that red supergiants can go missing as they turn into black holes—no supernovae required.
(Watch a black hole fall into a star and then blow it up.)
There’s more than one way to make stars vanish
Beasor and her colleagues also studied the same outburst in the Andromeda Galaxy. In a new pre-print analysis uploaded to arXiv.org, they outline why, based on data from Webb, it might not be a failed supernova after all.
The images suggest that some embers are still glowing at the source of the supposedly departed star—not what they’d expect from an insatiable void. Perhaps the initial pulse of light came from two stars merging into one, creating chaos and debris, but not a black hole. Afterward, lots of dust might have significantly dampened the light from the source. In other words, this could be a dust-shrouded star, or merger of stars, that's been misidentified.
Also, when a star collapses into a black hole, plenty of expelled matter should be plunging into its dark maw, which generates plenty of X-rays. But the space-based Chandra X-ray Observatory couldn’t find any. “The fact that you don’t see anything at all seems odd to me,” says Beasor.
De explains that gas initially takes a while to get pulled into a newly-made black hole, so you wouldn’t expect lots of X-ray emissions just yet—and that same gas would block any small, initial bursts of X-rays anyway.
For now, the existence of failed supernovae remains uncertain. Even if astronomers eventually decide that a candidate is the real deal, dust veils are still a good way to explain why some of the biggest red supergiants appear to be missing. “The failed supernovae thing wouldn’t be the only way to explain this,” says De.
Still, Webb has brought scientists loser to cracking the case than ever. Suresh and Kilpatrick already have their sights trained on other red supergiants that seem set for a supernova grand finale. It’ll be “interesting to see if any of those stars explode in the future,” says Suresh—or evaporate into nothingness.
