Simulating the Formation of Massive Protostars. I. Radiative Feedback and Accretion Disks

Abstract

We present radiation hydrodynamic simulations of collapsing protostellar cores with initial masses of 30, 100, and 200 M ⊙ . We follow their gravitational collapse and the formation of a massive protostar and protostellar accretion disk. We employ a new hybrid radiative feedback method blending raytracing techniques with flux-limited diffusion for a more accurate treatment of the temperature and radiative force. In each case, the disk that forms becomes Toomre-unstable and develops spiral arms. This occurs between 0.35 and 0.55 freefall times and is accompanied by an increase in the accretion rate by a factor of 2-10. Although the disk becomes unstable, no other stars are formed. In the case of our 100 and 200 M ⊙ simulation, the star becomes highly super-Eddington and begins to drive bipolar outflow cavities that expand outwards. These radiatively-driven bubbles appear stable, and appear to be channeling gas back onto the protostellar accretion disk. Accretion proceeds strongly through the disk. After 81.4 kyr of evolution, our 30 M ⊙ simulation shows a star with a mass of 5.48 M ⊙ and a disk of mass 3.3 M ⊙ , while our 100 M ⊙ simulation forms a 28.8 M ⊙ mass star with a 15.8 M ⊙ disk over the course of 41.6 kyr, and our 200 M ⊙ simulation forms a 43.7 M ⊙ star with an 18 M ⊙ disk in 21.9 kyr. In the absence of magnetic fields or other forms of feedback, the masses of the stars in our simulation do not appear limited by their own luminosities.

Disk-mediated accretion burst in a high-mass young stellar object

“…They allow further accretion to proceed even after the hydrogen burning starts 7 . At variance with low-mass protostars, the timescale for gravitational contraction (Kelvin-Helmholtz time) is shorter than the timescale for accretion in HMYSOs, producing a strong radiation field 25 .…”

“…Our burst detection proves the erratic behaviour of the accretion process in HMYSOs. Indeed, several radiation hydrodynamic simulations predict the onset of accretion variability in high-mass star formation 6,7,11 . Notably, episodic accretion might also play an important role in regulating the ionizing radiation, bloating the central source, and prolonging the accretion time during the Ultra-Compact H II (UCH II) phase 29 .…”

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

“…The accretion rate onto the star is similar to ours during the early phases of the calculation, and both show the accretion rate initially peaking after 5-10 kyr. However the Klassen et al (2016) shows a rapid growth in the accretion rate as the disc becomes gravitationally unstable. We attribute the difference to the fact we have fixed our protostar at the origin for the purpose of this first calculation, which will suppress gravitational instabilities that would otherwise enhance accretion.…”

“…Since we have adopted a novel radiative-transfer scheme for this calculation it is interesting to compare our results to other recent studies. Klassen et al (2016) studied high mass star formation by implementing the hybrid radiation transport scheme in the flash AMR hydrodynamics code. They started with spherical protostellar cores of 30 M , 100 M , and 200 M , with an ρ(r) ∝ r −3/2 density profile and the same solid body rotation as this study.…”

“…Tests of the method show that it does a remarkably good job of determining the dust temperature when compared to dedicated RT codes (Kuiper & Klessen 2013). Many contemporary studies now employ this hybrid method (Kuiper et al 2012;Klassen et al 2016;Rosen et al 2016).…”