2018A&A...615A.113M

Aims. The discovery of quasar J1342+0928 (z=7.54) reinforces the time compression problem associated with the premature formation of structure in Λ cold dark matter (ΛCDM). Adopting the Planck parameters, we see this quasar barely 690Myr after the big bang, no more than several hundred Myr after the transition from Pop III to Pop II star formation. Yet conventional astrophysics would tell us that a 10M_☉ seed, created by a Pop II/III supernova, should have taken at least 820Myr to grow via Eddington-limited accretion. This failure by ΛCDM constitutes one of its most serious challenges, requiring exotic "fixes", such as anomalously high accretion rates, or the creation of enormously massive (∼10⁵M_☉) seeds, neither of which is ever seen in the local Universe, or anywhere else for that matter. Indeed, to emphasize this point, J1342+0928 is seen to be accreting at about the Eddington rate, negating any attempt at explaining its unusually high mass due to such exotic means. In this paper, we aim to demonstrate that the discovery of this quasar instead strongly confirms the cosmological timeline predicted by the R_h=ct Universe.
Methods. We assume conventional Eddington-limited accretion and the time versus redshift relation in this model to calculate when a seed needed to start growing as a function of its mass in order to reach the observed mass of J1342+0928 at z=7.54.
Results. Contrary to the tension created in the standard model by the appearance of this massive quasar so early in its history, we find that in the R_h=ct cosmology, a 10M_☉ seed at z∼15 (the start of the Epoch of Reionization at t∼878Myr) would have easily grown into an 8x10⁸M_☉ black hole at z=7.54 (t∼1.65Gyr) via conventional Eddington-limited accretion.