Simulations of star formation with multigroup RHD and non-ideal MHD

Seminar Date: 
20 Oct 2015 - 10:30
Neil Vaytet

Stars form within turbulent complexes scaling hundreds of parsecs, harboring thousands of solar masses of cold gas: the molecular clouds. The generally accepted view that stars form by gravitational condensation of diffuse interstellar matter is very old; it is however only in recent decades that we have gained physical understanding of the process, thanks to ever more precise observations and complex numerical models.
Details of the collapse mechanism are however still debated. A dense clump of molecular gas (initially optically thin) is believed to contract isothermally as compression heating is radiated away, until the density is high enough to rescind the cooling. A hydrostatic body forms and accretes material from the surrounding envelope. Sustained increases in mass, density, and temperature eventually ignite nuclear fusion reactions: the star is born.
This multi-scale, multi-physics problem is very difficult to address through numerical modeling; the parent cloud scales 10,000 astronomical units (AU) while the protostar measures only 0.001 AU at birth. Many physical mechanisms, including magnetic fields, self-gravity, radiative transfer, and time dependent chemistry must be present in realistic models. PPSs in turn influence their vicinity through radiative feedback, jets and outflows, regulating the star formation process itself.
I will present two new advanced physical modules we have incorporated in our models of star formation over the past few years. The first is a multi-frequency radiation hydrodynamics solver, which enables one to take into account the large variations of dust and gas opacities as a function of frequency. It's application to 1D and 3D simulations will be discussed.
The second module improves our description of the interaction between the gas and magnetic fields by including additional resistive terms, which account for collisions between ions, neutrals and electrons. These are usually known as ambipolar and ohmic diffusion. I will show that they have a critical impact on the simulated structures of protostars, especially on the outflows and accretion discs.