Andromeda Star Vanishes: Astronomers Hypothesize Quiet Black Hole Collapse
A bright star in the nearby Andromeda galaxy has disappeared, leading astronomers to hypothesize it collapsed into a black hole. This event marks a potential observation of a rare stellar death.
Kishalay De, an astronomer with Columbia University and the Flatiron Institute, stated that the star was previously one of the brightest in the Andromeda galaxy but is now undetectable by most sensitive telescopes.
De and his colleagues reported their significant observations in the journal Science. They identified the disappearing star while reviewing 15 years of archival data from NASA's NEOWISE spacecraft, initially aiming to map changes in star brightness in infrared light.
The Disappearing Act
The star's transformation began around 2015 when it unexpectedly brightened for approximately a year. This surge was followed by a gradual fading in both infrared and optical light.
Within a few years, the star became completely invisible in optical light.
Known for decades and previously visible with small backyard telescopes, the star is now undetectable by the Hubble Space Telescope. It remains only faintly visible in infrared light with the advanced James Webb Space Telescope.
Evidence for a Black Hole
These observations align with the hypothesis that the star's internal nuclear reactor depleted its fuel, initiating a collapse into a black hole. The faint infrared glow that persists is attributed to residual stellar material falling into the nascent black hole. This gradual fading is expected to continue over the next few decades.
While massive stars typically conclude their lives in intensely bright, cataclysmic supernova explosions, theoretical astrophysicists propose that a star can also die by quietly collapsing into a black hole. This "quiet" collapse is a significantly less noticeable event.
Expert Insights and Alternative Views
Suvi Gezari, an astronomer not involved in the research, highlighted the study's importance. "The use of long-term infrared observations provides insights into a process often obscured by dust and faintness," she noted.
Another instance of an apparently disappearing star has been recorded, though it was more distant and fainter, limiting detailed observations. Christopher Kochanek, an astronomer who studied that similar event, stated that this approach—observing vanishing stars—is currently the primary method for detecting black hole formation.
Some astronomers propose an alternative explanation: these vanishing stars could be merging binary stars whose combined light then becomes obscured by a dense dust disk.
Further telescope observations over time are expected to provide clarity on the true nature of these disappearing celestial bodies.
Kochanek emphasized a crucial distinguishing factor for a black hole formation scenario: "The star must ultimately fade into complete darkness." This ultimate disappearance would differentiate it from other possibilities, such as merging binary stars temporarily obscured by dust.