Extreme Astrophysical Fluids, Magnetism and Radiation

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This proposal addresses problems related to i) extreme astrophysical magnetism; ii) the interaction of fluids with intense radiation fields; and iii) the physics of solid-gas mixtures during planet formation. The PI has published in all these areas with post-docs and students over the last few years.******1. Magnetars. We recently developed a 2-dimensional numerical model of a neutron star crust that incorporates elastic, plastic, magnetic and thermal effects. This model makes distinct predictions for the origin of the bright broad-band electromagnetic emission of magnetars, which is powered by the decay of 1015 G magnetic fields. We will develop detailed spectral models using newly calculated QED rates, and further explore the predictions of the 2D plastic-thermal model for the decaying dissipative tails seen following outbursts.******2. Gamma-ray bursts. We recently developed the first self-consistent model of the prompt (0.1-100s) phase of a GRB that i) starts with a strongly magnetized outflow and ii) uses kinetic calculations to reproduce key observational features (a narrow spectral peak, non-thermal spectra tail, and hard-to-soft evolution). Distinct predictions of spectral features are mirrored in some recent data, which will be investigated in more detail. ******3. Magnetized outflows containing intense radiation fields. We will investigate magnetocentrifugal flows from radiation-pressure dominated accretion disks, extending our previous calculations of jet acceleration. The wind torque will be calculated for a wide range of radial magnetic flux profiles, and applied to the global evolution of disks feeding hyper-accreting objects and supermassive black holes. ******4. Coherent low-frequency emission from relativistic outflows. Models of pulsar radio emission generally posit that the emitting plasma is confined to the magnetosphere. We will develop alternative processes involving relativistically expanded magnetized shells, which may be relevant to the fast radio burst phenomenon.******5. Origin of magnetic fields in compact stars. We recently investigated the pumping of magnetic helicity at convective-radiative boundaries in evolved stars. This process will be extended to accreting stars, to address the magnetization of recycled pulsars, cataclysmic variables, and young, massive stars.******6. Extreme solid-gas mixtures. The assembly of planets must involve extreme states in which solids dominate the mass density and gas the pressure. Our 2014 calculation of shock behavior, including a detailed account of particle fragmentation and melting, will be applied to planetesimal/planet disk interaction. The model of a two-phase proto-lunar disk developed by Thompson & Stevenson will be adapted to more general conditions, with a focus on the role of phase exchange in facilitating outflows. The particle solver in the publicly available code ATHENA will be updated to include fragmentation effects.