How accretion reshapes the rules for black hole reheating

Primordial black holes (PBHs) could, in principle, dominate the early Universe and reheat it entirely through Hawking evaporation — but accretion complicates that picture. By absorbing surrounding matter, PBHs grow heavier and prolong the matter-dominated era before they evaporate, altering the gravitational wave signal produced when they suddenly disappear. Big Bang nucleosynthesis bounds on that gravitational wave background then constrain the allowed PBH mass and initial abundance more tightly than previously estimated, shifting viable parameter space toward smaller formation masses. Merger-induced extended mass functions produce qualitatively similar shifts, though the gravitational-wave isocurvature constraint proves the more stringent of the two.