Astronomers document star’s vanishing act in rare ‘failed supernova’

Astronomers have captured what they describe as the most complete observational record of a massive star disappearing in what researchers interpret as a collapse into a black hole, without the dramatic supernova explosion that usually marks such stellar deaths.

The star, designated M31-2014-DS1, began brightening in infrared wavelengths in 2014 before dramatically fading over the following years. By 2023, it had become virtually invisible, dimming to one ten-thousandth of its original brightness in visible light. The remarkable observations, published Thursday in the journal Science, offer a rare glimpse into how some massive stars may end their lives.

“This star used to be one of the most luminous stars in the Andromeda Galaxy, and now it was nowhere to be seen,” said Kishalay De, an associate research scientist at the Simons Foundation’s Flatiron Institute who led the study, in a press release. “Imagine if the star Betelgeuse suddenly disappeared. Everybody would lose their minds! The same kind of thing [was] happening with this star.”

Mr. De and his team analyzed data from NASA’s NEOWISE project and other telescopes spanning nearly two decades, from 2005 to 2023. Located approximately 2.5 million light-years away in the neighboring Andromeda Galaxy, M31-2014-DS1 was a supergiant star roughly 100,000 times brighter than our sun.

The observations revealed an unusual pattern. Starting in 2014, the star’s infrared light increased by about 50% over two years. Then in 2016, it began swiftly dimming, becoming fainter than its original brightness within a year. The fading continued until the star essentially vanished from view.

When massive stars, those at least 10 times heavier than the sun, run out of fuel, gravity begins collapsing the core. Often this triggers a powerful shock wave that rips the star apart in a supernova explosion. But astronomers have long theorized that sometimes this shock wave fails, and most of the star’s material falls back onto the collapsing core, forming a black hole instead.

“We’ve known for almost 50 years now that black holes exist,” Mr. De said, “yet we are barely scratching the surface of understanding which stars turn into black holes and how they do it.”

The team’s analysis suggests M31-2014-DS1 represents this “failed supernova” scenario. Their models indicate the star had a final mass of roughly five times that of our sun, with about 98% of that material collapsing or falling back to form what the researchers conclude is a black hole. Less than about 0.1 solar mass — a small fraction of the star’s total mass — was likely expelled into space.

A key breakthrough came from understanding the role of turbulent convection in the star’s outer layers. Material near the star’s core is extremely hot, while outer regions are much cooler, creating churning motions similar to water boiling in a pot.

When the core collapsed, this swirling material didn’t fall directly into what the team says is a newly formed black hole. Instead, it orbited around it while slowly spiraling inward over decades, like water circling a drain rather than flowing straight down.

“The accretion rate is much slower than if the star imploded directly in,” said Andrea Antoni, a Flatiron Research Fellow and co-author, in the release. “Instead of taking months or a year to fall in, it’s taking decades.”

As this material moves away and cools, atoms and molecules combine to form dust. This dust absorbs light from the hot gas near the black hole and re-emits it in infrared wavelengths, creating a lingering red glow visible for decades after the star disappears.

Simulations suggest less than about 1% of material from the outer envelope accretes directly onto the black hole, but even this small amount powers the faint infrared light still detectable today.

The observations also helped the team reinterpret a similar star, NGC 6946-BH1, identified 10 years ago in the galaxy NGC 6946. That star followed a comparable pattern, suggesting these events may represent a distinct class of stellar deaths.

“It’s only with these individual jewels of discovery that we start putting together a picture like this,” Mr. De said.

The discovery provides observational evidence for theoretical models predicting that the relationship between a star’s birth mass and whether it forms a black hole may be complex and somewhat unpredictable. Using previous estimates, the researchers calculated they had between a 1% and 20% chance of finding such an event in their search of nearby galaxies.

Mr. De noted that light from the dusty debris surrounding the black hole will remain visible for decades to instruments like the James Webb Space Telescope.

“This is just the beginning of the story,” he said. “This may end up being a benchmark for understanding how stellar black holes form in the universe.”

The research was supported by NASA and the Simons Foundation. Observations were conducted using the Hubble Space Telescope, Spitzer Space Telescope and ground-based facilities including the MMT Observatory, Keck Observatory and Infrared Telescope Facility.