Magnetic fields in primordial accretion disks

¹ Sorbonne Universités, UPMC Univ. Paris 06, UMR 7095, Institut d’Astrophysique de Paris, 75014 Paris, France
e-mail: latif@iap.fr
² CNRS, UMR 7095, Institut d’Astrophysique de Paris, 75014 Paris, France
³ Departamento de Astronomía, Facultad Ciencias Físicas y Matemáticas, Universidad de Concepción, Av. Esteban Iturra s/n Barrio Universitario, Casilla 160-C, Chile

Received: 28 August 2015
Accepted: 3 November 2015

Abstract

Magnetic fields are considered a vital ingredient of contemporary star formation and may have been important during the formation of the first stars in the presence of an efficient amplification mechanism. Initial seed fields are provided via plasma fluctuations and are subsequently amplified by the small-scale dynamo, leading to a strong, tangled magnetic field. We explore how the magnetic field provided by the small-scale dynamo is further amplified via the α–Ω dynamo in a protostellar disk and assess its implications. For this purpose, we consider two characteristic cases, a typical Pop. III star with 10M_⊙ and an accretion rate of 10^-3M_⊙ yr^-1, and a supermassive star with 10⁵M_⊙ and an accretion rate of 10^-1M_⊙ yr^-1. For the 10M_⊙ Pop. III star, we find that coherent magnetic fields can be produced on scales of at least 100 AU, which are sufficient to drive a jet with a luminosity of 100L_⊙ and a mass outflow rate of 10^-3.7M_⊙ yr^-1. For the supermassive star, the dynamical timescales in its environment are even shorter, implying smaller orbital timescales and an efficient magnetization out to at least 1000 AU. The jet luminosity corresponds to ~10^6.0L_⊙ and a mass outflow rate of 10^-2.1M_⊙ yr^-1. We expect that the feedback from the supermassive star can have a relevant impact on its host galaxy.