The Entropy Budget of Primordial Black Hole Dark Matter

Black holes are the most entropic objects permitted by physics, carrying an entropy proportional to the area of their horizons that dwarfs, mass for mass, every other form of matter. If a substantial share of the dark matter consists of primordial black holes, the entropy budget of the observable universe changes character: instead of residing mainly in the photon bath, as it does in the standard accounting at roughly ten to the eighty-ninth in units of Boltzmann's constant, the bulk of the entropy would reside behind horizons. The headline computed values are: S total 30Msun = 2.13e+97; S per 30Msun = 2.65e+70. The work is computational throughout: assumptions are stated, the arithmetic is deposited, and no result is presented as a measurement.