Radiation pressure in super star cluster formation

Abstract

The physics of star formation at its extreme, in the nuclei of the densest and the most massive star clusters in the universe-potential massive black hole nurseries-has for decades eluded scrutiny. Spectroscopy of these systems has been scarce, whereas theoretical arguments suggest that radiation pressure on dust grains somehow inhibits star formation. Here, we harness an accelerated Monte Carlo radiation transport scheme to report a radiation hydrodynamical simulation of super star cluster formation in turbulent clouds. We find that radiation pressure reduces the global star formation efficiency by 30-35%, and the star formation rate by 15-50%, both relative to a radiation-free control run. Overall, radiation pressure does not terminate the gas supply for star formation and the final stellar mass of the most massive cluster is ∼ 1.3 × 10 6 M . The limited impact as compared to in idealized theoretical models is attributed to a radiation-matter anti-correlation in the supersonically turbulent, gravitationally collapsing medium. In isolated regions outside massive clusters, where the gas distribution is less disturbed, radiation pressure is more effective in limiting star formation. The resulting stellar density at the cluster core is ≥ 10 8 M pc −3 , with stellar velocity dispersion 70 km s −1 . We conclude that the super star cluster nucleus is propitious to the formation of very massive stars via dynamical core collapse and stellar merging. We speculate that the very massive star may avoid the claimed catastrophic mass loss by continuing to accrete dense gas condensing from a gravitationally-confined ionized phase.

Modeling UV Radiation Feedback from Massive Stars. III. Escape of Radiation from Star-forming Giant Molecular Clouds

“…The adaptive ray tracing calculates E i at every cell and keeps track of Q esc,i 3 These clouds are optically thick to UV radiation (Σ 0 κ −1 d,UV ∼ 10 M pc −2 ) but optically thin to dust-reprocessed IR radiation (Σ 0 κ −1 d,IR ∼ 10 3 M pc −2 ). The pressure from trapped IR radiation is likely to play a dominant role only for clouds in extremely high-surface density environments (e.g., Skinner & Ostriker 2015;Tsang & Milosavljević 2018). explicitly, allowing us to calculate the hydrogen absorption fraction, dust absorption fraction, and escape fraction defined as…”

Massive star feedback in clusters: variation of the FUV interstellar radiation field in time and space

“…a few times Solar). This latter regime was studied by Tsang & Milosavljević (2018) in a 10 7 M turbulent box, where radiation pressure only modestly reduced the star formation efficiency and rate, and did not disperse enough gas to stop star formation completely (helped by the porous gas distribution, in contrast with the Fall et al (2010) model). In short, the relatively low surface density and metallicity of our cloud (as well as the low luminosity) results in radiation pressure being unimportant as a source of feedback as it pertains to gas dispersal.…”

Two Thresholds for Globular Cluster Formation and the Common Occurrence of Massive Clusters in the Early Universe

“…The role of feedback in limiting the mass of a cluster is not clear. Ginsburg et al (2016) suggest that feedback has virtually no role and gas exhaustion stops star formation in the cluster, rather than gas expulsion (see also Girichidis et al 2012;Kruijssen 2012;Matzner 2017;Galván-Madrid et al 2017;Tsang & Milosavljević 2018;Silich & Tenorio-Tagle 2018;Cohen et al 2018;Ward & Kruijssen 2018). Also, there is no jump in the mass function of bound clusters at a mass of around 10 3 M ⊙ where ionization feedback suddenly increases as a result of the increasingly likely appearance of O-type stars (Vacca et al 1996).…”