2019/01/09 by Jon P. Ramsey, David A. Clarke
Physics and Astronomy · #Accretion (finance) #Astro and Planetary Science #Astrophysics #Astrophysics and Star Formation Studies #Bow shock (aerodynamics) #Classical mechanics #Computational physics #Jet (fluid) #Kinetic energy #Magnetic field #Magnetohydrodynamic drive #Magnetohydrodynamics #Mechanics #Physics #Protostar #RADIUS #Shock wave #Star formation #Stars #Stellar, planetary, and galactic studies #astro-ph.GA #astro-ph.HE #astro-ph.SR
paper · pdf · doi:10.1093/mnras/stz116
published as MNRAS, 484, 2364 (2019) · 26 pages, 16 figures. Accepted for publication in MNRAS
arxiv created 2019/01/09 · openalex publication_date 2019/01/10 · arxiv updated 2019/02/06 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We present 2.5D global, ideal magnetohydrodynamic (MHD) simulations of magnetically and rotationally driven protostellar jets from Keplerian accretion discs, wherein only the initial magnetic field strength at the inner radius of the disc, Bi, is varied. Using the AMR-MHD code AZEuS, we self-consistently follow the jet evolution into the observational regime (|\gt 103 au|) with a spatial dynamic range of ∼6.5 × 105. The simulations reveal a three-component outflow: (1) A hot, dense, super-fast, and highly magnetized ‘jet core’; (2) a cold, rarefied, trans-fast, and highly magnetized ‘sheath’ surrounding the jet core and extending to a tangential discontinuity; and (3) a warm, dense, trans-slow, and weakly magnetized shocked ambient medium entrained by the advancing bow shock. The simulations reveal power-law relationships between Bi and the jet advance speed, |v|jet, the average jet rotation speed, 〈|v|φ〉, as well as fluxes of mass, momentum, and kinetic energy. Quantities that do not depend on Bi include the plasma-β of the transported material that, in all cases, seems to asymptote to order unity. Jets are launched by a combination of the ‘magnetic tower’ and ‘bead-on-a-wire’ mechanisms, with the former accounting for most of the jet acceleration – even for strong fields – and continuing well beyond the fast magnetosonic point. At no time does the leading bow shock leave the domain and, as such, these simulations generate large-scale jets that reproduce many of the observed properties of protostellar jets including their characteristic speeds and transported fluxes.