Witnessing the birth of a supermassive protostar

Abstract

The detection of z > 6 quasars reveals the existence of supermassive black holes of a few 10 9 M ⊙ . One of the potential pathways to explain their formation in the infant universe is the so-called direct collapse model which provides massive seeds of 10 5 − 10 6 M ⊙ . An isothermal direct collapse mandates that halos should be of a primordial composition and the formation of molecular hydrogen remains suppressed in the presence of a strong Lyman Werner flux. In this study, we perform high resolution cosmological simulations for two massive primordial halos employing a detailed chemical model which includes H − cooling as well as realistic opacities for both the bound-free H − emission and the Rayleigh scattering of hydrogen atoms. We are able to resolve the collapse up to unprecedentedly high densities of ∼ 10 −3 g/cm 3 and to scales of about 10 −4 AU. Our results show that the gas cools down to ∼ 5000 K in the presence of H − cooling, and induces fragmentation at scales of about 8000 AU in one of the two simulated halos, which may lead to the formation of a binary. In addition, fragmentation also occurs on the AU scale in one of the halos but the clumps are expected to merge on short time scales. Our results confirm that H − cooling does not prevent the formation of a supermassive star and the trapping of cooling radiation stabilises the collapse on small scales.

The Birth of Binary Direct-collapse Black Holes

“…This approach enables us to follow the evolution of clumps that could become SMSs out to 3 Myr. Further details on our simulation setup and refinement criteria can be found in Latif et al (2016b) and Latif & Khochfar (2019).…”

Fragmentation inside atomic cooling haloes exposed to Lyman–Werner radiation

“…This scenario appears exceedingly difficult as the first stellar mass black holes are born "starving" (Whalen et al 2004;Alvarez et al 2009;Johnson et al 2011) in mini haloes which have been disrupted by both the ionising radiation from PopIII stars and the subsequent supernova explosions (Milosavljević et al 2009;Jeon et al 2014). As a direct result, investigation of supermassive star (SMS) formation as a viable alternative has been undertaken and appears attractive (Haiman 2006 Regan & Haehnelt 2009a,b;Volonteri 2010;Agarwal et al 2012Agarwal et al , 2013Agarwal et al , 2014Latif & Volonteri 2015;Latif et al 2016;Regan et al 2017). The larger initial seed masses of SMSs alleviate the growth requirements somewhat (Tanaka & Haiman 2009).…”

Rise of the first supermassive stars

“…Furthermore, ⋆ E-mail:john.regan@dcu.ie, Marie Skłodowska-Curie Fellow the remnants of Pop III stars continue to accrete very inefficiently even after migrating into larger haloes via mergers (Smith et al in prep). As a direct result, investigation of supermassive star (SMS) formation as a viable alternative has been undertaken and appears attractive (Haiman 2006;Begelman et al 2006;Wise et al 2008;Regan & Haehnelt 2009a,b;Volonteri 2010;Agarwal et al 2012Agarwal et al , 2013Agarwal et al , 2014Latif & Volonteri 2015;Latif et al 2016;Regan et al 2017).…”