On the effects of rotation in primordial star-forming clouds

Abstract

Context. The thermodynamical evolution of gas during the collapse of the primordial star-forming cloud depends significantly on the initial degree of rotation. Aims. However, there is no clear understanding of how the initial rotation can affect the heating and cooling process and hence the temperature that leads to the fragmentation of the gas during Population III star formation. Methods. We report the results from three-dimensional, smoothed-particle hydrodynamics (SPH) simulations of a rotating selfgravitating primordial gas cloud with a modified version of the Gadget-2 code, in which the initial ratio of the rotational to the gravitational energy (β 0 ) is varied over two orders of magnitude. Results. We find that despite the lack of any initial turbulence and magnetic fields in the clouds, the angular momentum distribution leads to the formation and build-up of a disk that fragments into several clumps. We further examine the behavior of the protostars that form in both idealized as well as more realistic minihalos from the cosmological simulations. The thermodynamical evolution and the fragmentation behavior of the cosmological minihalos are similar to that of the artificial cases, especially in those with a similar β 0 -parameter. Protostars with a higher rotation support exhibit spiral-arm-like structures on several scales, and have lower accretion rates. These type of clouds tend to fragment more, while some of the protostars escape from the cluster with the possibility of surviving until the present day. They also take much longer to form compared to their slowly rotating counterparts. Conclusions. We conclude that the use of appropriate initial conditions of the gas in minihalos is a pivotal and decisive quantity to study the evolution and final fate of the primordial stars.

Formation of metal-free binaries: Impact of H2 line cooling and CIE cooling

“…To avoid the "Courant catastrophe", we introduce sink particles inside the collapsing gas cloud once a certain density threshold is reached (Bate et al 1995;Bromm & Loeb 2004;Federrath et al 2010;Stacy et al 2010), as outlined in section 2. As mentioned in the introduction, in many of the previous works sink particles have been introduced at gas densities that correspond to the gas phase where H 2 line cooling still operates (Stacy et al 2010;Clark et al 2011b;Dutta 2016;Riaz et al 2018;Sharda et al 2019). The collapsing primordial gas is most susceptible to fragmentation at densities below 10 14 cm −3 (Hartwig et al 2015).…”

“…Many of the numerical simulations performed to understand the fragmentation behaviour of collapsing primordial gas and the resulting formation of single, binary, and multiple stellar systems have introduced sink particles (protostars) at a density 𝑛 H ≤ 10 13 cm −3 (Bromm & Loeb 2004;Moeckel & Bate 2010;Glover et al 2010;Stacy et al 2010;Hosokawa et al 2011;Stacy et al 2011Stacy et al , 2012Susa et al 2014;Dutta et al 2015;Dutta 2016;Riaz et al 2018;Sharda et al 2019;Sugimura et al 2020;Latif et al 2022). This is prior to the density threshold 𝑛 H ≥ 10 14 cm −3 where CIE cooling comes into play.…”

Formation of Supermassive Black Hole Seeds

“…Similarly, the dark matter halos with higher spin have a longer collapse timescale which results in enhanced fragmentation. Moreover, higher rotation decreases the mass accretion onto a protostar and consequently the final stellar mass gets reduced (Hirano et al 2014; Dutta 2016).…”

Formation of supermassive black hole seeds

“…Similarly, the dark matter halos with higher spin have a longer collapse timescale which results in enhanced fragmentation. Moreover, higher rotation decreases the mass accretion onto a protostar and consequently the final stellar mass gets reduced (Hirano et al 2014;Dutta 2016).…”