A pair of recent papers aim to illuminate one of cosmology’s most enduring mysteries: the true nature of dark matter, the elusive substance thought to make up 80% of the universe’s mass.
Stefano Profumo, a professor at the University of California, Santa Cruz, proposes bold, testable frameworks that trace the origin of dark matter to known physical principles. While dark matter has yet to be directly observed, measurements of the universe’s structure at the largest scales, as well as measurements of the cosmic background radiation, support theoretical expectations for its existence.
Mysterious Origins
Understanding how dark matter came to be would mark a significant step toward unraveling its nature. Profumo’s work explores the possibility that dark matter is a natural byproduct of the early universe, rather than the result of a more recent or exotic phenomenon. He speculates that dark matter may have emerged in a sort of “mirror world” composed of unique particles and forces—following the same physical laws as our universe, yet remaining invisible to humans.
His hypothesis draws inspiration from quantum chromodynamics (QCD), the theory that describes the bond between quarks inside protons and neutrons. In a parallel “dark QCD,” Profumo proposes that dark quarks and gluons could bind together through a dark strong force to form dark baryons. These dark baryons, he suggests, might have reached sufficient mass and density to collapse into tiny, stable black holes—or at least black hole-like objects.
Explaining Invisible Dark Matter
Although only a few times heavier than the fundamental mass scale of quantum gravity, these dark black holes could potentially account for all of the dark matter inferred to exist—if they formed frequently enough. A compelling aspect of this idea is that it could explain why dark matter has remained undetected. These black holes would be invisible to particle detectors, yet their gravitational influence would be felt across the cosmos.
Because they would interact solely through gravity, they would evade detection by conventional means. Yet their presence could still help shape the large-scale structure of the universe. Profumo’s new framework relies on established physics, offering a testable hypothesis that doesn’t require introducing new particles beyond the Standard Model.
Cosmic Horizon
In a second paper, Profumo puts forward an entirely different theory: that dark matter may be produced by the cosmic horizon—the outer boundary of the observable universe. Similar to a black hole’s event horizon but on a much larger scale, the cosmic horizon may have generated dark matter through a brief burst of expansion following cosmic inflation. This concept is based on quantum field theory in curved spacetime.
According to the paper, if the proper temperature and energy ratio were reached during this phase—and assuming dark matter is stable and gravitationally produced—then it could have been radiated into existence. The concept is inspired by thermal radiation phenomena that appear near event horizons.
“Both mechanisms are highly speculative, but they offer self-contained and calculable scenarios that don’t rely on conventional particle dark matter models, which are increasingly under pressure from null experimental results,” said Profumo.
He noted that this latest work builds upon a long legacy of theoretical research at UC Santa Cruz, including contributions to the Lambda Cold Dark Matter model of the universe.
“And they do so in a way that remains rooted in known physics—whether quantum field theory in curved spacetime, or the well-studied properties of SU(N) gauge theories—while extending them to new frontiers,” Profumo said.
The paper “Dark Baryon Black Holes” appeared on May 9, 2025, and the paper “Dark Matter From Quasi–de Sitter Horizons” appeared July 8, 2025, both in Physical Review D.
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.