In 2019, celestial observers documented an unusual occurrence emanating from a celestial body situated at a considerable cosmic distance.
For a duration spanning approximately one hour, its luminosity experienced a subtle yet distinct augmentation before reverting to its typical quiescent state.
This observed behavior deviated from established stellar phenomena; it was too protracted for a typical stellar flare, too ephemeral for a supernova event, and lacked the characteristic irregularity associated with most recognized forms of stellar variability.
Following a meticulous investigation into the characteristics of this anomaly, scientists now propose that it may represent a signature from one of the universe’s most enigmatic entities: an infinitesimally small primordial black hole, possessing a mass equivalent to merely three of our planet’s moons.
A black hole of such modest mass would possess an event horizon approximately commensurate in size with the terminal punctuation mark of this sentence.
A consortium of astrophysicists, spearheaded by Renee Key from Swinburne University of Technology in Australia, asserts that no alternative explanation aligns as competently with the statistical profile of the incident, consequently bestowing upon the purported black hole the appellation ‘Phoebe’.
“Phoebe suggests the existence of a multitude of compact, lunar-mass entities intertwined with the distribution of dark matter within the Milky Way, and potentially unlocks novel avenues for investigating the fundamental physics of cosmic inflation,” the research group articulated in a preliminary paper submitted to arXiv.
Our conventional understanding of black holes typically categorizes them as exceedingly massive and substantial objects, with their masses commencing at a minimum of several solar masses and escalating to tens of billions of solar masses.
This perception is largely dictated by their formative processes, which originate from the catastrophic demise of colossal stars, whose immense cores subsequently undergo gravitational collapse, thereby giving rise to one of the most densely packed structures known within the cosmos.
However, in the nascent moments following the Big Bang, conditions may have been propitious for the genesis of considerably more diminutive black holes. Quantum fluctuations within the fabric of spacetime could have engendered regions of heightened density in the expanding universe, which subsequently collapsed in a manner analogous to the core collapse of a star today.
These hypothetical celestial bodies are designated as primordial black holes, and their existence, to date, remains confined to theoretical frameworks.
This theoretical status may be attributable to their inherent difficulty in detection. A primordial black hole with a mass equivalent to Earth’s would exhibit a diameter of merely 1.8 centimeters (0.7 inches).
Even if such a diminutive black hole were to exhibit an accretion event, the intense radiation emitted by matter ensnared by its gravitational pull would register as an almost imperceptible glimmer – rendering it undetectable from Earth with our current observational apparatus.
Yet, this is not the sole modality through which a primordial black hole might be identified.
Even with remarkably small physical extents, the gravitational influence surrounding these entities would be sufficiently formidable to distort spacetime in the vicinity of their event horizons.
This region of severely warped spacetime can function as a cosmic lens, magnifying any background light that traverses it, resulting in a transient, gentle increase in brightness before a return to baseline levels – a phenomenon characterized as microlensing.
This precisely mirrors the type of signal that the Dark Energy Camera (DECam) registered in 2019 when its attention was directed towards the Large Magellanic Cloud, a galaxy situated approximately 163,000 light-years from our planet.
The anomaly transpired on December 18th, during a five-night observational period executed by DECam as part of the Asteroid-Mass Primordial black hole Microlensing (AMPM) survey.
Over the course of approximately 60 minutes, the luminosity of a star within the Large Magellanic Cloud demonstrably increased, notwithstanding the stable brightness of its adjacent stellar neighbors.
While microlensing events are infrequent, they are not unprecedented. Previously observed microlensing events have been ascribed to stellar-mass black holes, diminutive, faint stars and their associated planetary companions, or rogue exoplanets traversing interstellar space independently of any stellar host.
To ascertain whether Phoebe could indeed be a black hole, the investigative team first undertook the crucial task of eliminating potential confounding factors such as instrumental errors, stellar flares, interference from other stellar sources, and intrinsic stellar luminosity variations.
Subsequently, they proceeded to construct models for various microlensing scenarios: a free-floating exoplanet within the Milky Way; a free-floating exoplanet residing in the Large Magellanic Cloud; and a primordial black hole situated within the Milky Way’s diffuse dark matter halo, at a distance from the galaxy’s denser material concentration.
According to their rigorous computations, the lensing entity, Phoebe – irrespective of its precise nature – exhibits an improbability of five orders of magnitude greater for originating from the Milky Way’s dark matter halo than from known stellar populations within either galaxy.
The most compelling hypothesis posits Phoebe as a primordial black hole, possessing approximately three times the mass of the Moon, and located at an estimated distance of 59,630 light-years.
This conclusion does not entirely dismiss the possibility of a rogue exoplanet inhabiting the Milky Way’s halo. Indeed, the proposition of a rogue exoplanet remains a viable contender, particularly considering that, from an observational standpoint, rogue exoplanets are generally considered to be more prevalent and thus more likely to be detected.
However, within the sparsely populated expanse of the Milky Way’s halo, a black hole is statistically more probable than a rogue exoplanet, given that the latter are typically theorized to be more abundant in regions characterized by a high density of stars.
This recent discovery surfaces amidst a prevailing scientific discourse.
In February 2026, a collaborative effort between researchers in the United States and Japan, who analyzed data acquired by the Subaru Telescope, identified twelve potential microlensing candidates directed towards the Andromeda galaxy, which they suggested could be indicative of primordial black holes.
Subsequently, a distinct research group affiliated with the University of Warsaw in Poland undertook a re-evaluation of the identical dataset and published their counterargument in March, concluding that each of these events could be readily attributed to conventional, well-understood stellar objects.
This newly presented finding provides substantial support for one side of this ongoing debate.
Key and her associates contend that their observations corroborate the initial interpretation of the Subaru data, which indicated that the observed events are consistent with the characteristics of primordial black holes.
This situation invariably points to a singular imperative: the necessity for a more advanced and sensitive generation of telescopes.
“Our detection findings offer compelling motivation for the microlensing initiatives at the Roman and Vera C. Rubin Observatories to implement high-cadence, static observation strategies, thereby enhancing the sensitivity to microlenses of lower mass,” the research team states in their publication.
We eagerly anticipate the advancements to come.
The preliminary scientific manuscript is accessible via arXiv.
