In 2019, astronomers recorded a distant star in the Large Magellanic Cloud unexpectedly brightening for about an hour, a behavior unlike any known stellar phenomenon. After detailed analysis, researchers suggest this unusual flare could be the signature of a primordial black hole, an elusive object formed in the early universe, potentially revealing a hidden population of tiny, moon-mass black holes. The findings are detailed in a preprint posted to arXiv, highlighting a rare glimpse into a mysterious corner of the cosmos.
A Star That Defied Expectations
For roughly sixty minutes, the light from a star located 163,000 light-years away gently surged before returning to normal. Its brightness curve didn’t match typical stellar flares, supernovae, or known variability patterns. The unusual signal was captured by the Dark Energy Camera (DECam) as part of the Asteroid-Mass Primordial black hole Microlensing (AMPM) survey.
Lead astronomer Renee Key and her team at Swinburne University of Technology explored multiple possibilities, from instrumental glitches to ordinary stellar behavior. “Phoebe suggests a population of compact, lunar-mass objects associated with the dark matter distribution of the Milky Way, and potentially opens a new window to the physics of inflation,” the team writes in a preprint posted to arXiv. Their modeling strongly points to a tiny black hole, roughly three times the mass of the Moon, temporarily bending the light of the background star in a phenomenon known as microlensing.
Primordial Black Holes: A Window Into the Early Universe
Unlike typical black holes formed from collapsing stars, primordial black holes could have emerged from quantum fluctuations in the universe just after the Big Bang. These objects are tiny by comparison, with event horizons smaller than a marble. Detecting them directly is nearly impossible; even if they consumed surrounding matter, the resulting light would be almost undetectable.
However, their gravitational influence can act as a cosmic lens. When a primordial black hole passes in front of a distant star, it magnifies the star’s light briefly, creating a telltale brightening. This is exactly what DECam observed with the event now nicknamed Phoebe. Such detections could provide critical clues to the nature of dark matter and the early universe.
Microlensing And The Search For Hidden Mass
Microlensing events are rare, but they offer a unique way to detect objects otherwise invisible. Key and her colleagues ran extensive simulations to rule out alternative explanations, including rogue exoplanets and dim stars. According to their analysis, Phoebe is five orders of magnitude more likely to belong to the Milky Way’s dark matter halo than to any known stellar population.
This discovery adds weight to ongoing debates over the existence of primordial black holes. Earlier 2026 studies using the Subaru Telescope suggested potential microlensing events in Andromeda could be due to similar objects, although some teams argued these could be explained by ordinary stars. Phoebe strengthens the case for small black holes hiding in galactic halos and opens the door for future observations with high-precision telescopes.
