The aftermath of the first stars: massive black holes

We investigate the evolution of the primordial gas surrounding the first massive black holes formed by the collapse of Population III stars at redshifts z ≳ 20 . Carrying out three‐dimensional hydrodynamical simulations using gadget , we study the dynamical, thermal and chemical evolution of the first relic H  ii regions. We also carry out simulations of the mergers of relic H  ii regions with neighbouring neutral minihaloes, which contain high‐density primordial gas that could accrete on to a Population III remnant black hole. We find that there may have been a significant time delay, of the order of ∼10 8 yr, between black hole formation and the onset of efficient accretion. The build‐up of supermassive black holes, believed to power the z ≳ 6 quasars observed in the Sloan Digital Sky Survey, therefore faces a crucial early bottleneck. More massive seed black holes may thus be required, such as those formed by the direct collapse of a primordial gas cloud facilitated by atomic line cooling. The high optical depth to Lyman–Werner (LW) photons that results from the high fraction of H 2 molecules that form in relic H  ii regions, combined with the continued formation of H 2 inside the dynamically expanding relic H  ii region, leads to shielding of the molecules inside these regions at least until a critical background LW flux of ∼10 −24 erg s −1 cm −2 Hz −1 sr −1 is established. Furthermore, we find that a high fraction of deuterium hydride (HD) molecules, X HD ≳ 10 −7 , is formed, potentially enabling the formation of Population II.5 stars, with masses of the order of ∼10 M ⊙ , during later stages of structure formation when the relic H  ii region gas is assembled into a sufficiently deep potential well to gravitationally confine the gas again.