An unstable truth: how massive stars get their mass

Abstract

The pressure exerted by massive stars' radiation fields is an important mechanism regulating their formation. Detailed simulation of massive star formation therefore requires an accurate treatment of radiation. However, all published simulations have either used a diffusion approximation of limited validity; have only been able to simulate a single star fixed in space, thereby suppressing potentially-important instabilities; or did not provide adequate resolution at locations where instabilities may develop. To remedy this we have developed a new, highly accurate radiation algorithm that properly treats the absorption of the direct radiation field from stars and the re-emission and processing by interstellar dust. We use our new tool to perform three-dimensional radiation-hydrodynamic simulations of the collapse of massive pre-stellar cores with laminar and turbulent initial conditions and properly resolve regions where we expect instabilities to grow. We find that mass is channeled to the stellar system via gravitational and Rayleigh-Taylor (RT) instabilities, in agreement with previous results using stars capable of moving, but in disagreement with methods where the star is held fixed or with simulations that do not adequately resolve the development of RT instabilities. For laminar initial conditions, proper treatment of the direct radiation field produces later onset of instability, but does not suppress it entirely provided the edges of radiation-dominated bubbles are adequately resolved. Instabilities arise immediately for turbulent pre-stellar cores because the initial turbulence seeds the instabilities. Our results suggest that RT features are significant and should be present around accreting massive stars throughout their formation.

Formation and Evolution of Disks Around Young Stellar Objects

“…However, it remains an open question as to what exact extent disk fragmentation contributes to the multiplicity properties of high-mass star forming regions. Disk formation and fragmentation around forming massive protostars has been studied in only a few three-dimensional simulation studies which include radiation transport to properly render the thermodynamics of the (un)stable disk (Krumholz et al 2007(Krumholz et al , 2009Kuiper et al 2011;Rosen et al 2016;Klassen et al 2016;Meyer et al 2017Meyer et al , 2018Rosen et al 2019).…”

A statistical spectropolarimetric study of Herbig Ae/Be stars

“…Even the most recent, sophisticated star formation models are not able to simulate the fine detail required to probe the accretion process from parsec scales via an accretion disk to the stellar surface. For example, Rosen et al (2016) explicitly mention that the material is not followed in the inner 80 au. Given that our spectropolarimetric evidence points towards circumstellar disks that are present at very small scales, the logical, direct conclusion we can draw is that the disk is not truncated, but reaches all the way down to the stellar surface.…”

Thermal Feedback in the High-mass Star- and Cluster-forming Region W51

“…Generally, these models produce a highmass star with enough luminosity to halt further spherical accretion at a very early stage, with *~ -MM 10 20 . Radiation pressure provides a fundamental limit on how much mass can be accreted (Wolfire & Cassinelli 1987;Osorio et al 1999), but geometric effects can circumvent this limit and allow further accretion (Yorke & Sonnhalter 2002;Krumholz et al 2005Krumholz & Matzner 2009;Kuiper & Yorke 2013;Rosen et al 2016). Additionally, fragmentationinduced starvation can limit the amount of mass available to the most massive star, instead breaking up massive cores into many lower-mass fragments (Peters et al 2010b;Girichidis et al 2012), though other simulations suggest that feedback should suppress this fragmentation (Myers 2013;Krumholz et al 2016).…”