Astronomers have documented a rare celestial event: the near-total disappearance of a massive star in the Andromeda galaxy, designated M31-2014-DS1, without the expected explosive finale of a supernova. This observation challenges existing models of stellar death and black hole formation, suggesting that some massive stars may collapse directly into black holes with minimal outward energy release.
A Star’s Quiet Demise
The star, once a luminous giant in Andromeda, now appears as a faint red remnant surrounded by expanding dust. Observations spanning several years, meticulously pieced together by Kishalay De at Columbia University, revealed a steady fading of the star’s brightness beginning around 2020, following an initial brightening in 2014. This pattern strongly suggests a “failed supernova” – a theoretical scenario where gravity overwhelms outward pressure, causing the star to collapse inward without a significant explosion.
Detecting such events is inherently difficult. The vast distances involved, coupled with the presence of dust and the crowded nature of star fields, can easily obscure or misrepresent observations. The prolonged fading of M31-2014-DS1, however, distinguished it from other potential causes of dimming, such as the star being temporarily hidden behind a cloud of debris.
Dust and Gas Reveal Clues
The dust surrounding the remnant blocked much of the visible light, but it radiated heat in the infrared spectrum. Data from the James Webb Space Telescope revealed that this dusty shell extends approximately 4 to 19 billion miles from the star’s former location – a distance far exceeding the expected radius of any surviving stellar remnant. As the dust cooled, it formed grains that further thickened the shroud, causing the remnant to appear increasingly red over time.
Further analysis revealed a shell of gas expanding outward at around 60 miles per second. This outflow, containing roughly one-tenth the mass of our Sun, indicates that the star did eject some material before or during its collapse. Low-energy models of stellar collapse predict that a collapsing core can indeed expel a portion of its outer layers, creating a faint, dusty outflow. However, the presence of this gas doesn’t definitively confirm either a failed supernova or an alternative explanation.
The Search for a Black Hole Signal
Typically, the formation of a black hole is accompanied by accretion – the process of gas falling into the black hole, heating up to extreme temperatures, and emitting intense X-rays. Surprisingly, independent analysis of the region around M31-2014-DS1 revealed no detectable X-ray source, even with deep observations. This absence weakens the case for a black hole actively feeding on surrounding material, as accretion usually produces significant X-ray emissions.
However, the lack of X-rays isn’t conclusive. Dense gas can absorb X-rays and re-emit them as heat, potentially masking the signal. The absence of X-rays doesn’t entirely rule out the possibility of a black hole at the core of the remnant.
A Stellar Merger as an Alternative?
Another possible explanation for the star’s disappearance is a stellar merger – a collision between two stars. Such events can produce a brief flare of light followed by a prolonged period of dust obscuration. Dr. Emma Beasor of Liverpool John Moores University noted that the signatures of a failed supernova can closely resemble those produced by a stellar merger, making it difficult to distinguish between the two scenarios through dusty clouds alone.
If a merger occurred, a surviving star might still reside within the dust cloud, and the fading process could eventually stabilize rather than continue indefinitely. Definitive proof would require either detecting the black hole actively accreting material or definitively ruling out the presence of any surviving star as the dust thins.
Implications for Black Hole Formation
The significance of failed supernova candidates lies in their potential to reshape our understanding of black hole formation. If these quiet collapses are common, the number of black holes in the universe may be significantly higher than previously estimated based on supernova counts. This would necessitate adjustments to existing stellar evolution models.
A previous survey identified another disappearing giant, N6946-BH1, which also faded from view leaving behind a faint glow. Continued observations with advanced telescopes like the James Webb Space Telescope will be crucial for monitoring these remnants and determining whether the light continues to fade, as predicted by the collapse scenario.
What’s Next for M31-2014-DS1?
Astronomers will continue to monitor M31-2014-DS1 as the dust gradually disperses, allowing more light from the central region to escape. Repeated observations will measure whether the warm glow continues to fade or if it brightens, and whether any high-energy signals eventually emerge. A late detection of X-rays would strongly support the collapse scenario, while a stable or increasing output would suggest the presence of a surviving star within the dust.
For now, M31-2014-DS1 remains a cosmic puzzle, poised at the boundary between a quiet black hole birth and a messy stellar collision. Further observations promise to shed light on the ultimate fate of this once-bright star and refine our understanding of the diverse ways in which massive stars meet their end.
The study is published in arXiv.
