Accreting Primordial Black Holes: Dark Matter Constituents

This paper shows that accretion of positronium plasma between 0.01 to 14s after the Big Bang could have created small black holes contributing at least 1 percent of the dark matter present today, with uncertainties ranging from 10 percent or more. General relativistic magnetohydrodynamic (GRMHD) simulations newly adapted to the early Universe confirm that accretion is due to magneto-rotational instability (MRI) in a rotating plasma. By contrast with Bondi accretion producing primordial masses bigger than the Sun, MRI could produce masses 10^15-18 g observable by their Hawking radiation contributing to background gamma rays.