Protostellar collapse: radiative and magnetic feedbacks on small scale fragmentation

TL;DR

This study uses advanced simulations to show that radiative transfer and magnetic fields significantly influence the collapse and fragmentation of prestellar cores, emphasizing the need for their inclusion in realistic star formation models.

Contribution

It provides the first consistent AMR simulation of a 1 solar mass core including both magnetic fields and radiative transfer, highlighting their combined effects on collapse and fragmentation.

Findings

Radiative transfer significantly affects core temperature and fragmentation.

Magnetic fields inhibit fragmentation even with radiative transfer included.

Numerical resolution and solver robustness are crucial for reliable results.

Abstract

It is established that both radiative transfer and magnetic field have a strong impact on the collapse and the fragmentation of prestellar dense cores, but no consistent calculation exists yet at such scales. We present original AMR calculations including magnetic field (in the ideal MHD limit) and radiative transfer, within the Flux Limited Diffusion approximation, of the collapse of a 1 solar mass dense core. We compare the results with calculations performed with a barotropic EOS. We show that radiative transfer has an important impact on the collapse and the fragmentation, through the cooling or heating of the gas, and is complementary of the magnetic field. A larger field yields a stronger magnetic braking, increasing the accretion rate and thus the effect of the radiative feedback. Even for a strongly magnetized core, where the dynamics of the collapse is dominated by the magnetic field, radiative transfer is crucial to determine the temperature and optical depth distributions, two potentially accessible observational diagnostics. A barotropic EOS cannot account for realistic fragmentation. The diffusivity of the numerical scheme, however, is found to strongly affect the output of the collapse, leading eventually to spurious fragmentation. Both radiative transfer and magnetic field must be included in numerical calculations of star formation to obtain realistic collapse configurations and observable signatures. Nevertheless, the numerical resolution and the robustness of the solver are of prime importance to obtain reliable results. When using an accurate solver, the fragmentation is found to always remain inhibited by the magnetic field, at least in the ideal MHD limit, even when radiative transfer is included.