Growth problems of stellar black holes in early galaxies

Abstract

The nature of the seeds of the observed high-z super-massive black holes (SMBH) is unknown. Although different options have been proposed, involving e.g. intermediate mass direct collapse black holes, BH remnants of massive stars remain the most natural explanation. To identify the most favorable conditions (if any) for their rapid growth, we study the accretion rate of a M • = 100M BH formed in a typical z = 10 galaxy under different conditions (e.g. galaxy structure, BH initial position and velocity). We model the galaxy baryonic content and follow the BH orbit and accretion history for 300 Myr (the time span in 10 > z > 7), assuming the radiation-regulated accretion model by Park & Ricotti (2013). We find that, within the limits of our model, BH seeds cannot grow by more than 30%, suggesting that accretion on light-seed models are inadequate to explain high-z SMBH. We also compute the X-ray emission from such accreting stellar BH population in the [0.5 − 8] keV band and find it comparable to the one produced by high-mass X-ray binaries. This study suggests that early BHs, by X-ray pre-heating of the intergalactic medium at cosmic dawn, might leave a specific signature on the HI 21 cm line power spectrum potentially detectable with SKA.

Gravitational stability and fragmentation condition for discs around accreting supermassive stars

“…They can grow SMBHs in the available time if either with continuous accretion at the Eddington limit or with short episode of super-Eddington growth. In reality, E-mail: r.matsukoba@astr.tohoku.ac.jp however, the BH's growth can easily be hindered by its own radiative feedback (Milosavljević et al 2009;Park & Ricotti 2011;Sugimura et al 2018;Orofino et al 2018). An alternative and attractive pathway for seed BH formation is via the so-called direct collapse (e.g., Bromm & Loeb 2003), where a supermassive star (SMS) with ∼ 10 5 M collapses into a BH with a similar mass by general relativistic instability (Umeda et al 2016;Woods et al 2017;Haemmerlé et al 2018).…”

Massive black holes in high-redshift Lyman Break Galaxies

“…Seeding prescriptions employing stellar mass BH (M• < ∼ 10 2 M ) seeds are known to face difficulties in explaining the observed 10 9 M SMBHs at z = 6 (Alvarez et al 2009;Orofino et al 2018). Such models have to resort to prolonged super-Eddington accretion phases (Madau et al 2014;Volonteri et al 2015;Aversa et al 2015;Lupi et al 2016;Regan et al 2019;Takeo et al 2020), in contrast with models in which radiation pressure regulates gas infall, such as e.g.…”