Researchers scanning 15 years of NASA NEOWISE infrared observations say a once‑bright star in the Andromeda galaxy abruptly brightened around 2015, faded steadily in both infrared and optical bands, and is now undetectable in visible light. The lead author, Kishalay De of Columbia University and the Flatiron Institute, reports the source is “nowhere to be seen” in Hubble imaging and only marginally present in James Webb Space Telescope infrared data. The team published their findings in Science and interprets the pattern as consistent with a massive star exhausting its nuclear fuel and collapsing directly into a black hole without a bright supernova. Alternative explanations exist, and astronomers stress that follow‑up observations over years to decades will be needed to confirm whether the object truly faded into permanent darkness.
Key Takeaways
- Archival NEOWISE infrared data spanning roughly 15 years were searched to map stellar brightness changes; one Andromeda star stood out for dramatic variation.
- The source brightened around 2015 for about one year, then declined rapidly in both infrared and optical wavelengths and is now absent in optical surveys.
- Hubble Space Telescope imaging currently detects no optical counterpart; James Webb Space Telescope reports only a very faint infrared signal.
- Authors propose a direct collapse (a “failed supernova”) into a black hole as the simplest interpretation of the light curve and remaining infrared emission.
- Not all experts are convinced; competing hypotheses include a stellar merger whose light is later obscured by a dust disk.
- Published in the journal Science and reported via NEOWISE archival work, the case offers one of the best candidates yet for witnessing black hole formation.
- Confirmation requires continued monitoring: if the source continues to fade toward undetectability, that would favor the direct‑collapse scenario.
Background
Massive stars typically end their lives in bright supernova explosions that can briefly outshine their host galaxy, making such deaths relatively easy to spot across extragalactic distances. Theoretical models, however, predict that some high‑mass stars may instead undergo a direct collapse: the star’s core fails to launch an outgoing shock and the star implodes to form a black hole with little or no luminous display. Observational searches for these “failed supernovae” have relied on long‑term imaging so that the sudden disappearance of a previously visible star can be recognized.
The NASA NEOWISE mission, designed to survey the sky in infrared wavelengths, has produced a rich archival dataset covering roughly 15 years. That archive enables systematic searches for long‑term infrared variability that can reveal transients obscured in optical light by dust or intrinsically faint at visible wavelengths. Andromeda (M31), our nearest large galactic neighbor, has been monitored by numerous surveys and telescope facilities, providing ancillary optical and high‑resolution imaging needed to evaluate candidates.
Main Event
The object in question was historically among the brighter stars in Andromeda and was visible from modest amateur setups in past decades. When the NEOWISE team inspected time‑series infrared photometry, they flagged it as an outlier: a roughly yearlong brightening event around 2015 followed by a pronounced decline. Optical follow‑up showed the source fading to invisibility a few years after the infrared peak.
Kishalay De and colleagues cross‑checked archival optical data and contemporary Hubble imaging; Hubble currently records no optical counterpart at the star’s coordinates. James Webb Space Telescope observations detect only a faint infrared residual, orders of magnitude dimmer than the historical brightness. The remaining infrared glow could be sustained by some material continuing to accrete onto a compact remnant, or by dust warmed by remnant heat.
The authors argue that the timeline—the brief luminous episode, rapid multiwavelength decline, and current near‑absence of emission—is what one would expect if a massive star ran out of fuel and collapsed directly into a black hole, producing little to no classical supernova display. They quantify the brightness changes and note the event contrasts with typical supernova light curves that peak very brightly and then decay on different timescales.
Analysis & Implications
If the direct‑collapse interpretation holds, this object would provide one of the clearest observational windows into black hole birth in a nearby galaxy. That would help calibrate rates of failed supernovae, which in turn inform stellar evolution models and predictions for the birth mass distribution of stellar black holes. Better empirical rates would also constrain population synthesis models used to predict gravitational‑wave event rates from binary black hole mergers.
On the other hand, alternative scenarios carry different astrophysical implications. A stellar merger obscured by newly formed or ejected dust would produce a temporary brightening and then optical disappearance as dust absorbs and re‑radiates light in the infrared. That pathway implies different progenitor populations and dust production mechanisms, with consequences for interpreting transient sky surveys.
Practically, the case highlights the power of long‑baseline infrared archives like NEOWISE combined with high‑resolution follow‑up from Hubble and JWST. Infrared monitoring opens access to phenomena hidden by dust or intrinsically faint at optical wavelengths, expanding the discovery space beyond classical bright transients. Over the next years, systematic searches of NEOWISE and continued JWST/Hubble checks could increase the sample of candidate direct collapses or rule out individual cases.
Comparison & Data
| Property | Andromeda candidate (NEOWISE) | Previously reported disappearing star |
|---|---|---|
| Distance | ~780 kpc (Andromeda) | Greater (more distant) |
| Peak behaviour | Brightened ~2015 for ~1 year, then faded | Similar fade but fainter historically |
| Optical detection | Currently none in Hubble imaging | Also absent or marginal |
| Infrared | Very faint residual in JWST | Too faint for detailed follow‑up |
The table summarizes qualitative contrasts: the Andromeda candidate benefits from proximity (~780 kpc) and richer archival coverage, yielding stronger multiwavelength constraints than the more distant, fainter previously reported case. That improved data quality is why researchers call this one of the best candidates so far, though it is not a perfect twin of earlier examples.
Reactions & Quotes
Team members and outside researchers emphasize both the excitement and the need for caution. The lead analyst framed the observational surprise and the challenge of testing the interpretation.
“It used to be one of the brightest stars in the Andromeda galaxy; today it is nowhere to be seen,”
Kishalay De (Columbia University / Flatiron Institute)
Another astronomer not on the paper praised the use of long infrared baselines to reveal events obscured or too faint for optical surveys, while noting the interpretive hurdles that remain.
“Long‑term infrared monitoring opens a window on processes hidden by dust and faint in visible light,”
Suvi Gezari (University of Maryland)
A senior researcher who has studied a prior disappearing star laid out the key observational test—permanence of disappearance—and mentioned an alternative dust‑obscuration route that must be ruled out.
“The decisive signature for a black hole is that the source fades to permanent darkness; other explanations, like merging stars cloaked by dust, remain plausible until ruled out,”
Christopher Kochanek (Ohio State University)
Unconfirmed
- The direct‑collapse interpretation remains a best‑fit explanation but is not yet proven; continued fading would strengthen it.
- Alternative scenarios—most notably a stellar merger followed by dust formation that hides the merged object—could reproduce the observed light curve in some models.
- The origin of the faint infrared residual (accretion onto a compact object versus warm dust) has not been definitively identified.
Bottom Line
This Andromeda object represents a leading candidate for a black hole forming via direct collapse because of its recorded brightening around 2015, subsequent rapid fade in both infrared and optical bands, and current absence in Hubble optical imaging paired with only a faint JWST infrared signal. If further monitoring shows a continued decline toward permanent invisibility, the case for a failed supernova that produced a newborn black hole will strengthen significantly.
However, the scientific verdict is not yet final: plausible alternative explanations remain, and only sustained, multi‑instrument follow‑up over years to decades can robustly distinguish permanent collapse from transient obscuration. Whatever the outcome, the event demonstrates how archival infrared surveys like NEOWISE plus targeted follow‑up with Hubble and JWST can reveal rare, otherwise hidden endpoints of stellar evolution.
Sources
- NPR report on the discovery (news media)
- NASA NEOWISE mission page (official NASA mission/archival data)
- James Webb Space Telescope (JWST) (official observatory)
- Hubble Space Telescope (official observatory)
- Science journal (peer‑reviewed journal; paper referenced by the research team)