An international team of astronomers says the source of elusive dark matter may be even stranger than previously suspected, with new research exploring a possible connection to the fifth dimension.
In a recent paper published in Physical Review D, researchers from Lehman College, CUNY Graduate Center, the IceCube Neutrino Observatory, and the Max Planck Institute propose that hypothetical primordial black holes may have formed with five-dimensional properties, potentially offering new insights into the mystery of dark matter.
While a theory linking such exotic concepts may sound far-fetched, the researchers say their work has potential observational implications, including a possible connection to an unusually energetic neutrino detection.
Since astronomers first identified evidence of unseen mass in the early 20th century, including pioneering observations by Jan Oort and Fritz Zwicky, scientists have struggled to understand the mysterious substance.
Dark Matter
Dark matter is a mysterious form of matter that, according to prevailing cosmological models, makes up the majority of matter in the universe. Yet exactly what dark matter is remains the subject of considerable debate. The “dark” in its name refers to the fact that it does not emit, absorb, or reflect detectable light, rendering it effectively invisible.
So far, evidence for dark matter has come primarily from its gravitational effects on visible matter and light. Researchers have proposed numerous explanations for what dark matter might be and where it originates, although none has been conclusively established. The new research explores one particularly unusual possibility involving black holes formed during the universe’s earliest moments.
The Fifth Dimension
The new work builds on the dark dimension scenario proposed by Miguel Montero, Cumrun Vafa, and Irene Valenzuela in 2023, which sought to address questions involving dark energy and string theory.
Their work explored how a hypothetical additional spatial dimension might help reconcile the observed properties of dark energy with theoretical constraints arising from quantum gravity. String theory, a theoretical framework in which fundamental constituents of nature are described as tiny vibrating strings, allows for additional dimensions beyond the familiar three dimensions of space and one of time.
The resulting scenario describes a universe with five dimensions rather than the four we ordinarily experience. Although the extra dimension remains hypothetical, researchers have continued investigating its potential implications for cosmology and fundamental physics.
Fifth Dimensional Dark Matter
The international team’s new work explores the possibility that this fifth dimension is a genuine feature of our universe. In the proposed scenario, the additional spatial dimension would extend over a microscopic distance, potentially on the order of a micron, far smaller than the thickness of a human hair.
According to the researchers, primordial black holes formed in the early universe could possess five-dimensional properties, fundamentally changing how they behave compared with conventional four-dimensional black holes.
The study examines several proposed mechanisms for primordial black hole formation, including cosmic inflation, early-universe phase transitions, and cosmic strings. Within the theoretical framework considered, the researchers find that these mechanisms would generally produce five-dimensional primordial black holes.
Importantly, some of these hypothetical—particularly those formed from cosmic strings—could survive for periods comparable to the age of the universe.
Such long-lived primordial black holes have attracted interest as potential contributors to dark matter, although neither their existence nor the proposed fifth dimension has been confirmed.
The researchers also identify a possible connection between their model and an extraordinarily energetic neutrino detected by the KM3NeT observatory in 2023. The particle’s energy is intriguingly close to a fundamental energy scale predicted by the five-dimensional framework.
Earlier research explored whether radiation emitted by evaporating five-dimensional primordial black holes could account for such unusual neutrino events. However, this remains a theoretical interpretation rather than an established explanation for the observation.
Future observations of high-energy neutrinos, along with additional constraints on primordial black holes and extra-dimensional physics, could help scientists evaluate these ideas.
The paper, “Primordial Black Holes are Five-Dimensional,” appeared in Physical Review D on September 28, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.