In 2014, astronomers were treated to an unusual celestial display: M31-2014-DS1, a hydrogen-depleted supergiant located in the nearby Andromeda Galaxy, began to show noticeable brightening at mid-infrared wavelengths.
That changed just a few years later, however. Beginning in 2017, the star curiously began fading to a significant degree—enough so that by 2022, it was virtually undetectable in the overall light it cast.
“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. “Imagine if the star Betelgeuse suddenly disappeared. Everybody would lose their minds!”
“The same kind of thing [was] happening with this star in the Andromeda Galaxy,” De said.
Now, data from NASA’s NEOWISE mission has provided astronomers with what could finally be a resolution to this cosmic cold case, revealing the most complete observations of a star collapsing into a black hole ever recorded, allowing them to assemble a new class of events connecting a series of cosmic “oddballs.”
From these observations of a black hole’s birth, researchers have now developed a more comprehensive understanding of how these transformations occur, as revealed in a recent paper published in Science. The team behind the discovery combined recent observations with archival data dating back more than ten years to refine models that explain how some stars collapse into black holes rather than explode as supernovae.
“This is just the beginning of the story,” De, who is also the lead author of a new paper describing the work, said in a recent statement.
Strange Stellar Activity
The event occurred in the Andromeda galaxy, roughly 2.5 million light-years away. The dead star was designated M31-2014-DS1 and had been under the eye of NEOWISE and other telescopes since 2005. It wasn’t until 2014 that astronomers noticed any interesting activity, when the star began to brighten, before it rapidly dropped below its original luminosity.
Further observations in 2022 and 2023 revealed an even more dramatic dimming, to the point that the star was almost undetectable in visible and near-infrared light.
Nonetheless, according to De, the faint light around the black hole “is going to be visible for decades at the sensitivity level of telescopes like the James Webb Space Telescope, because it’s going to continue to fade very slowly.”
He adds that “this may end up being a benchmark for understanding how stellar black holes form in the universe.”
The Birth of a Black Hole
After comparing the rapid and dramatic dimming to theoretical models, they identified that the star had likely collapsed into a black hole.
Black holes form when a massive star’s gravitational forces become imbalanced toward the end of its life. These stars have at least ten times the mass of our Sun and have experienced a gravitational tug-of-war between inward- and outward-directed forces. In these cases, as the star runs out of fuel, the inward forces gain the upper hand, collapsing the star into a dense neutron star. From here, the process can go in one of two directions.
In the first case, an explosive supernova occurs as the neutrino emissions result in a shockwave that rips the star apart. The theoretical alternative is that if a shockwave proves incapable of pushing the stellar material outwards, it will instead collapse into a black hole.
“We’ve known for almost 50 years now that black holes exist,” says De, “yet we are barely scratching the surface of understanding which stars turn into black holes and how they do it.”
Similar Black Hole Events
Not content simply to identify the event as the birth of a black hole, the team broadened its research. They looked at archival observations of the star NGC 6946-BH1 through the lens of what they had discovered with M31-2014-DS1. This provided the team with the context needed to better understand the events involving the second star.
Previously, researchers had ignored the influence of convection, the process that occurs when extreme temperature differences within the star, comprising a hotter core and cooler outer layers, push gases towards the cooler outer layers. Convection keeps those gases moving, even as the core collapses, preventing most of the outer layers from falling in, eventually forming a dust cloud. Hot gases surrounding the black hole then warm the dust, which becomes visible to astronomers as a red glow decades after a star’s final moments.
“The accretion rate—the rate of material falling in—is much slower than if the star imploded directly in,” explained co-author Andrea Antoni. “This convective material has angular momentum, so it circularizes around the black hole. Instead of taking months or a year to fall in, it’s taking decades. And because of all this, it becomes a brighter source than it would be otherwise, and we observe a long delay in the dimming of the original star.”
The team also identified similar behavior in the star NGC 6946-BH1, and in their continuing work, their aim is to identify an entirely new category of events based on what were once considered cosmic “oddballs.”
“It’s only with these individual jewels of discovery that we start putting together a picture like this,” De said.
The paper, “Disappearance of a Massive Star in the Andromeda Galaxy Due to the Formation of a Black Hole,” appeared in Science on February 12, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.