Temperature evolution of low-mass PBHs vs. cosmic temperature. In the radiation-dominated era, PBHs of mass 10⁻²³ M_⊙ (denoted m23) and higher, if they form, do so on the green diagonal line and evolve with little mass loss until Ṁ is of the same order as M, at which point they rapidly heat and evaporate. Kelvin units are used at the top and right borders. PBHs change their evolutionary rate as T ∼ M⁻¹, from radiation (solid line), to matter (dashed line), to dark-energy dominated (dotted line). The t8 line marks the start of galaxy formation. The three dotted vertical lines are from left to right the QCD transition at 220 MeV, the surface of last scattering of the CMB, and the temperature today, 2.7 K.