A new preprint study from researchers at Oakland University and Rice University questions whether primordial black holes (PBHs) with asteroid-scale masses could be hiding in the cosmic gamma-ray glow and explain dark matter. PBHs, theorized to have formed from collapsing matter just after the Big Bang, have long been a candidate for the universe's missing mass. The paper casts doubt on this scenario for that specific class of tiny black holes.
Primordial black holes differ from stellar-mass black holes, which result from dying star collapses. Astrophysicists have proposed that PBHs, spanning a wide range of masses from microscopic to asteroid-sized, might constitute dark matter. The new analysis focuses only on asteroid-mass PBHs, using gamma-ray emissions as a constraint mechanism to test their existence.
The study examines the isotropic gamma-ray background observed by telescopes. The authors argue that if asteroid-mass PBHs were abundant enough to account for dark matter, they would produce detectable gamma-ray signatures through Hawking radiation—a prediction not matched by current observations. This finding narrows the allowable mass range for such objects.
This work challenges a key hypothesis tying PBHs to dark matter, but it does not rule out all primordial black holes. Larger or smaller PBHs may still exist and could behave differently. The paper is a preprint on arXiv and has not yet undergone peer review, meaning its conclusions remain provisional.
If confirmed, the results would redirect dark matter research toward other candidates like weakly interacting massive particles (WIMPs) or axions. The study also highlights how multi-messenger astronomy—combining gamma-ray data with theoretical models—can test even exotic cosmological ideas.