Effect of Population III multiplicity on dark star formation

Abstract

We numerically study the mutual interaction between dark matter (DM) and Population III (Pop III) stellar systems in order to explore the possibility of Pop III dark stars within this physical scenario. We perform a cosmological simulation, initialized at z∼ 100, which follows the evolution of gas and DM. We analyse the formation of the first minihalo at z∼ 20 and the subsequent collapse of the gas to densities of 1012 cm−3. We then use this simulation to initialize a set of smaller scale ‘cut‐out’ simulations in which we further refine the DM to have spatial resolution similar to that of the gas. We test multiple DM density profiles, and we employ the sink particle method to represent the accreting star‐forming region. We find that, for a range of DM configurations, the motion of the Pop III star–disc system serves to separate the positions of the protostars with respect to the DM density peak, such that there is insufficient DM to influence the formation and evolution of the protostars for more than ∼5000 years. In addition, the star–disc system causes gravitational scattering of the central DM to lower densities, further decreasing the influence of DM over time. Any DM‐powered phase of Pop III stars will thus be very short‐lived for the typical multiple system, and DM will not serve to significantly prolong the life of Pop III stars.

Gravitational wave background from Population III binaries

“…Numerical simulations of the collapse of rotating metal-free clouds indicate the appearance of a bar instability leading to the formation of two protostars in a binary (Saigo et al 2004). In recent simulations (Turk et al 2009;Stacy et al 2010;Greif et al 2011;Clark et al 2011;Stacy et al 2012), a similar result was shown. A massive protostellar cloud develops spiral structure, instabilities, and leads to the formation of several multiple systems.…”

Weakly Interacting Massive Particle Dark Matter and First Stars: Suppression of Fragmentation in Primordial Star Formation

“…As our models do not include the effects of ionisation feedback from massive stars, we stopped our simulation at this point. However, we note that studies that have investigated the effect of this ionisation feedback find that it rapidly shuts off the supply of material to the disc, and hence will act to suppress fragmentation at later times (Stacy et al 2012;Hosokawa et al 2011).…”

“…This issue has been addressed recently by Stacy et al (2012), who performed a calculation in which they resimulated the inner regions of a halo with a live DM halo of similar resolution to that of the gas after the formation of an initial sink particle. The effects of DMA were not, however, included.…”

“…However, the scope of these results was limited as the maximum resolvable density in the Ripamonti et al (2010) study was reached before a hydrostatic object was formed. In complementary work, Stacy et al (2012) addressed the phases after the formation of a hydrostatic object, adopting an ad-hoc prescription for the earlier phase. These authors found that if multiple protostars were present, dynamical interactions would displace them from the DM density peak, thereby removing them from the region where DMA would have the most influence.…”

First stars and WIMP dark matter: A state of the art review

“…However, all of the latter lack the right resolution to resolve the DM cusp inside it, and actually "switch off" DM after (or sometimes even before) the formation of a hydrostatic object, as a consequence of the fact that the gravitation potential become totally dominated by the baryons in a standard scenario. A recent study, [10], has explored the sub-resolution domain including a hyperrefined DM particle population, originally set with a cusp distribution. It was found that the original DM cusp got modified by the formation of the fragments, and that there is a displacement between the center of the DM cusp (whose profile remains radial in good approximation) and the position of the most massive hydrostatic object.…”