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Astronomers have debunked claims that a lunar-mass primordial black hole was detected in the Large Magellanic Cloud. A reanalysis of data from the Dark Energy Camera (DECam), led by researchers Andrzej Udalski and Przemek Mr.óz of the University of Warsaw, confirms that the star “Phoebe” is a naturally variable star rather than a target of gravitational microlensing. The findings, published in June 2026 on the arXiv preprint server, show that the star’s repeated brightness fluctuations align with established stellar behavior, effectively ruling out the existence of a primordial black hole (PBH) in that specific observation.
Why was Phoebe mistaken for a black hole?
In May 2026, a separate research team identified a brief flicker of light from a star and interpreted it as a microlensing event. Microlensing occurs when a compact, invisible object—such as a primordial black hole—passes directly between Earth and a distant star, temporarily magnifying the star’s light. Because the brightening lasted less than an hour, the original researchers calculated that the lensing object must have possessed the mass of the moon. This interpretation relied on the assumption that the event was a singular, non-repeating gravitational interaction.
How did researchers prove the star is a variable?
Udalski and Mr.óz utilized a broader dataset that included public DECam observations from 2020 and 2021, which were absent from the initial study. Their analysis revealed that the star brightened at least three times over several years. Because these light variations repeated, they could not have been caused by a single, one-time passage of a primordial black hole. To confirm these fluctuations were intrinsic to the star, the team monitored two nearby stars of similar brightness; those stars remained steady, proving that the flickering was unique to the star’s own cycle.
What do these findings mean for dark matter research?
The reanalysis restores consistency with data from the Optical Gravitational Lensing Experiment (OGLE). OGLE has monitored this region of the sky for years with high precision and has not detected the thousands of microlensing events that would be expected if lunar-mass primordial black holes accounted for a significant portion of dark matter in the Milky Way’s halo. According to Udalski and Mr.óz, the case serves as a cautionary tale: short-term observations lasting only a few days are often insufficient to differentiate between exotic gravitational events and the common, natural variability of stars.
Did you know?
Primordial black holes are hypothetical objects thought to have formed in the first fraction of a second after the Big Bang. If they exist, they could potentially explain the mystery of dark matter, but current observational evidence remains elusive.
Frequently Asked Questions
- What is a primordial black hole?
It is a theoretical type of black hole that formed in the high-density environment of the early universe, rather than from the collapse of a star. - Why is the star considered a variable star?
The star exhibits repeated, non-random changes in brightness over several years, a characteristic behavior of common variable stars, whereas microlensing events are singular and unrepeatable. - Is there any evidence for primordial black holes?
While they remain a popular candidate for dark matter, no definitive evidence has been confirmed through microlensing surveys like OGLE, which continue to place strict limits on their potential abundance.
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