Tiny black holes explain galaxy flows and the expansion of the Universe express
Dark matter may not be particles but black holes from the Big Bang era. In the early Universe, which was like a swirling batter, they were like heavy lumps — barely moving, they gathered surrounding matter and spun it into the swift galaxy flows astronomers observe today. But there's a twist: the lightest holes, according to Hawking's theory, evaporate, emitting energy. This evaporation gently warms the cosmic 'batter' in its early stages, thereby changing the calculated rate of the Universe's expansion and smoothing out the notorious tension between different measurement methods.
Original abstract
as written by the authors arXiv:2601.07106
The high value of the cosmic microwave dipole may be telling us that dark matter is macroscopic rather than a fundamental particle. The possible presence of a significant dark matter component in the form of primordial black holes suggests that dark halo formation simulations should be commenced well before redshift z = 100. Unlike standard CDM candidates, PBHs behave as dense, non-relativistic matter from their inception in the radiation-dominated era. This allows them to seed gravitational potential wells and begin clustering earlier. We find that starting N-body simulations at redshifts even before matter-radiation equality yield galaxy bulk flow velocities that are systematically larger than those predicted by standard LCDM models. The early, high-mass concentrations established by PBHs lead to a more rapid and efficient gravitational acceleration of surrounding baryonic and dark matter, generating larger peculiar velocities that remain coherent over scales of hundreds of Mpc. Furthermore, a sub-population of PBHs in the 10^-20 to 10^-17 solar mass range would lose a non-negligible fraction of their mass via Hawking radiation over cosmological timescales. This evaporation process converts matter into radiation, so a time-varying matter density parameter, Omega_m', is introduced, which behaves like a boosted radiation term in the Friedmann equation. This dynamic term acts to reduce the Hubble tension. A higher effective Omega_r in the early universe reduces the sound horizon at the epoch of recombination. PBH mass loss also influences fits to the equation of state parameter, w, at low redshift. The naive N-body modelling presented here suggests investigation with tried and tested cosmology codes should be carried out, by introducing mass losing PBHs and starting the evolution as early as practicable.
One such hole weighs as much as an asteroid but is compressed to a point smaller than an atomic nucleus. Its evaporation is so unhurried that over the entire history of the Universe, it would lose only a minuscule fraction of its mass.