Formation of SMBH seeds in Pop III star clusters through collisions : the importance of mass loss

TL;DR

This study investigates how mass loss during protostar collisions affects the formation of supermassive black hole seeds in Population III star clusters, showing that mass loss significantly reduces the final mass but still allows seed formation.

Contribution

It introduces the impact of collision-induced mass loss into models of SMBH seed formation in primordial star clusters, a factor previously neglected.

Findings

Mass loss can reduce the final SMBH seed mass by 15-80%.

Even with mass loss, seeds of about 10^4 solar masses can form.

Massive enough to serve as SMBH seeds despite mass loss effects.

Abstract

Runaway collisions in dense clusters may lead to the formation of supermassive black hole (SMBH) seeds, and this process can be further enhanced by accretion, as recent models of SMBH seed formation in Population III star clusters have shown. This may explain the presence of supermassive black holes already at high redshift, $z>6$. However, in this context, mass loss during collisions was not considered and could play an important role for the formation of the SMBH seed. Here, we study the effect of mass loss, due to collisions of protostars, in the formation and evolution of a massive object in a dense primordial cluster. We consider both constant mass loss fractions as well as analytic models based on the stellar structure of the collision components. Our calculations indicate that mass loss can significantly affect the final mass of the possible SMBH seed. Considering a constant mass loss of 5% for every collision, we can lose between 60-80% of the total mass that is obtained if mass loss were not considered. Using instead analytical prescriptions for mass loss, the mass of the final object is reduced by 15-40%, depending on the accretion model for the cluster we study. Altogether, we obtain masses of the order of $10^4M_{\odot}$, which are still massive enough to be SMBH seeds.