For years, a luminous blue star in Andromeda pulsed faintly, then slipped below the reach of ordinary telescopes. Astronomers argue this quiet disappearance marks a rare direct stellar collapse into a remnant.
The vanishing star lurked inside routine survey images, its fading light buried among millions of unremarkable stellar points. Careful reanalysis of infrared data turned that ghostly trace into evidence of a failed supernova event and ongoing stellar black hole formation within this Andromeda galaxy observation itself. What other quiet endings lie unnoticed?
How astronomers stumbled on a vanished star in Andromeda
Several years after NASA’s WISE spacecraft had scanned Andromeda, researchers rechecked the infrared frames and saw that a brilliant point of light had simply gone missing. They cross‑matched those frames with the ongoing NEOWISE infrared survey and, by mining archival space data, realised that a catalogued star had faded entirely past the limits of detection.
The light curve showed the star brightening in infrared around 2014 before sliding into optical darkness, a behaviour that initially looked like a data glitch from a crowded region of the Andromeda Galaxy. Later, a targeted Andromeda monitoring campaign revealed it as a rare transient sky event tied to collapse.
What makes M31-2014-DS1 so unusual among dying stars
M31‑2014‑DS1 had long stood out as a bright blue star on images of Andromeda, shining enough to be used as a reference point for photometric calibrations. Follow‑up spectra later showed this massive progenitor star had lost most of its outer layers, leaving a stripped stellar envelope behind.
Under standard theory, such a compact, luminous object should end its life in a spectacular supernova, blasting its outer layers into surrounding space with an intense flash. Instead, observers saw rapid dimming that matched a failed core collapse scenario, where energy leaks into neutrinos and produces the unusual stellar fading now linked to black‑hole birth.
This has probably been the most surprising discovery of my career, because the signature of the disappearing star was sitting in public data sets for years before anyone recognised what it meant.
Kishalay De
The infrared afterglow that revealed a failed supernova
NEOWISE watched the Andromeda Galaxy every six months, following the source known as M31-2014-DS1 from 2014 to 2017 as it brightened in infrared light while its visible glow weakened. Astronomers linked this slow fading to heated grains and infrared dust emission around it.
Models indicate that gas from the stripped star spiraled into the newborn black hole, releasing energy close to the collapsing core. That power likely formed an accretion disk signature that heated dust into thermal dust radiation, producing a long-lasting afterglow which observatories like JWST might still detect decades after collapse.
Competing explanations: direct collapse or stellar merger ?
Astronomers do not all share the view that M31-2014-DS1 slipped quietly into a black hole. A group answered Kishalay De’s preprint by advancing a stellar merger hypothesis, arguing that two stars in Andromeda combined and expelled gas, imitating the infrared of a failed supernova.
Data from NEOWISE arrive only every six months, so the most frantic stage of the outburst in Andromeda may have passed unrecorded by the spacecraft. Those gaps leave room for alternative astrophysical models, and the resulting observational uncertainties keep open direct collapse or intricate interaction within a system.
“Unlike finding supernovae, which is easy because the supernova outshines its entire galaxy for a few weeks, finding individual stars that disappear without producing an explosion is remarkably difficult.”
Kishalay De
What this event tells us about how stellar black holes form
Across competing theories of stellar death, the 2014 event in Andromeda sharpens how astronomers picture the birth of stellar black holes. A 13-solar-mass star, reduced by winds to roughly five Suns, appears to have vanished, telling us our census of the black hole population tied to failed neutrino-driven explosions remains stubbornly incomplete.
Models for stellar death now look less secure, since a star squarely in the usual mass bracket for a bright supernova appears to have slipped straight into a dark remnant. For theorists, revised core collapse thresholds and new massive star evolution pathways must explain winds, rotation, and metallicity.
Looking back at Andromeda’s quiet history of stellar deaths
Written accounts and photographic plates from the late 19th and early 20th centuries portray M31 as a remarkably quiescent galaxy in terms of stellar cataclysms. The solitary 1885 outburst, labelled S Andromedae, still anchors the official Andromeda supernova record and shapes expectations for massive-star deaths there seen from Earth.
Infrared monitoring of M31-2014-DS1 hints that many quiet stellar endings escaped notice when telescopes focused almost entirely on optical flashes. Future re-analyses of archived plates and digital images from historical sky surveys may uncover rare stellar transients that marked unseen black hole births in Andromeda over the decades.
