Seeds of supermassive black holes in general relativistic and alternative cosmologies: Implications of massive seeds

TL;DR

This paper investigates the formation and growth of supermassive black holes in various cosmological models, emphasizing primordial seeds and accretion processes, to explain high-redshift SMBHs observed by JWST.

Contribution

It introduces a comprehensive analysis of SMBH seed formation across different cosmologies and evaluates the impact of primordial black holes on dark matter and galaxy evolution.

Findings

Massive seeds ($ ext{≥}10^4 M_ ext{sun}$) enable SMBH growth by z=10 in all models.

Super-Eddington accretion can produce SMBHs from stellar-mass seeds in all cosmologies.

Primordial black holes contribute minimally to dark matter for masses ≥ $10^7 M_ ext{sun}$.

Abstract

Presence of supermassive black holes (SMBHs) with mass $(10^{6}-10^{9}) M_{\odot}$ at $z = 10$ has been recently revealed by James Webb Space Telescope (JWST) observations. In this study we generate seeds for the above range of SMBHs in various background cosmologies. We consider cosmic timescales required for black hole growth provided by three general relativistic cosmological models ($\Lambda$CDM, $\omega$CDM and Dynamical Dark Energy(DDE) and the braneworld cosmology. The growth of SMBHs is studied through Eddington limited and super-Eddington accretion, where the accretion starts at z=30. It is found that growth of SMBHs by z=10 within Eddington limited accretion is possible through massive seeds $(M\geq10^{4}M_{\odot})$ in all cosmologies. Super Eddington accretion onto spinning black holes with mass of few tens of solar masses can result in SMBHs by z=10 in all cosmologies. The viable cosmologies considered here are found to be unable to strongly distinguish between the seed black hole masses. The seeds generated in this work are assumed to be of primordial origin in order to satisfy the criteria of formation of high redshift massive galaxies. The fraction of primordial black holes (PBHs) contributing to dark matter ($f_{PBH}$) and their corresponding number densities for the mass range ($10^{5}-10^{8}$) $M_{\odot}$ are calculated in both seed effect and Poisson effect. In seed effect, PBHs of mass $\geq 10^{7} M_{\odot}$ contributes $\leq 10^{-2}$ to the dark matter fraction. The evolution of gas mass inside a PBH seeded dark matter halo is studied. The ratio of black hole to stellar mass is also evaluated for star formation efficiency in the range (0.1-1) and found to be ($10^{-3}-1$) for $M_{BH}=10^{8} M_{\odot}$ and ($10^{-2}-10$) for $M_{BH}=10^{9} M_{\odot}$.