Radiation-hydrodynamical simulations of massive star formation using Monte Carlo radiative transfer – II. The formation of a 25 solar-mass star

Abstract

We present a numerical simulation of the formation of a massive star using MonteCarlo-based radiation hydrodynamics (RHD). The star forms via stochastic disc accretion and produces fast, radiation-driven bipolar cavities. We find that the evolution of the infall rate (considered to be the mass flux across a 1500 au spherical boundary), and the accretion rate onto the protostar, are broadly consistent with observational constraints. After 35 kyr the star has a mass of 25 M and is surrounded by a disc of mass 7 M and 1500 au radius, and we find that the velocity field of the disc is close to Keplerian. Once again these results are consistent with those from recent high-resolution studies of discs around forming massive stars. Synthetic imaging of the RHD model shows good agreement with observations in the near-and far-IR, but may be in conflict with observations that suggests that MYSOs are typically circularly symmetric on the sky at 24.5 µm. Molecular line simulations of a CH 3 CN transition compare well with observations in terms of surface brightness and line width, and indicate that it should be possible to reliably extract the protostellar mass from such observations.

Monte Carlo radiative transfer

“…Many of the applications primarily aim to calculate synthetic observables but MCRT methods are also used to determine physical and/or dynamical conditions in complex multidimensional geometries, such as star forming environments, disc-like structures, nebulae or circumstellar material configurations (e.g. Wood et al 1996;Och et al 1998;Bjorkman and Wood 2001;Ercolano et al 2003;Kurosawa et al 2004;Ercolano et al 2005;Carciofi and Bjorkman 2006;Altay et al 2008;Carciofi and Bjorkman 2008;Ercolano et al 2008;Pinte et al 2009;Harries 2011;Haworth and Harries 2012;Harries 2015;Hubber et al 2016;Lomax and Whitworth 2016;Harries et al 2017). MCRT schemes have also found use in astrophysical problems that require a general relativistic treatment of radiative transfer processes (e.g.…”

“…Haworth and Harries (2012) investigated triggered star formation with a RH approach in which the gas temperature is adjusted by a MC-based photo-ionization calculation. Harries (2015) and Harries et al (2017) continued the development of MC-based RH methods for star formation problems. Noebauer et al (2012) and Roth and Kasen (2015) introduced MC-based RH techniques with a general-purpose scope, with a particular focus on IMC techniques in the latter.…”

Radiation hydrodynamic simulations of massive star formation via gravitationally trapped H ii regions – spherically symmetric ionized accretion flows

“…In some scenarios, however, the midplane regions are so dense that they are shielded from radiation. Consequently, accretion onto the star through these regions would not be halted by ionization feedback, but by some other process (Nakano 1989;Yorke & Sonnhalter 2002;Krumholz et al 2009;Kuiper et al 2010;Harries et al 2017;Kuiper & Hosokawa 2018).…”

Observing substructure in circumstellar discs around massive young stellar objects

“…Numerical simulations have demonstrated that feedback can be overcome by accretion through a disc (e.g. Kuiper et al 2010Kuiper et al , 2011Klassen et al 2016;Rosen et al 2016;Harries et al 2017), with the feedback energy escaping through the poles. Therefore, circumstellar discs are pivotal in allowing massive stars to grow, and so characterising them observationally is key.…”

“…To date, some synthetic observations have been computed from dynamical simulations of massive star formation/disc evolution, and are generally very optimistic about the detection of substructure in discs (e.g. Krumholz et al 2007;Harries et al 2017;Meyer et al 2018). However, these studies typically place objects at nearby distances (≤1 kpc), do not always account for the full instrumentational (e.g.…”