Astrophysics Seminar

NASA’s NICER telescope has recently provided evidence for non-dipolar magnetic field structures in rotation-powered millisecond pulsars. These stars are assumed to have gone through a prolonged accretion spin-up phase, begging the question of what accretion flows onto stars with complex magnetic fields would look like. In this talk, I will be discussing results from a suite of axisymmetric general relativistic magnetohydrodynamic (GRMHD) simulations of accreting neutron stars for dipole, quadrupole, and quadrudipolar stellar field geometries. We find that the location and size of the accretion columns resulting in hotspots change significantly depending on initial stellar field strength and geometry. The simulations inform on the variability properties of the hotspots, which can aid in future pulse-profile modeling of accreting sources. We also find that the strongest contributions to the stellar torque are from disk-connected fieldlines and the pulsar wind, leading to spin-down in almost all of the parameter regime we explored. The disk collimates the initial open stellar flux forming jets. We find that the disk-magnetosphere interaction significantly influences the net jet power and show that our model provides a viable mechanism to explain the observed radio jet power both in the low- and high-magnetic field case.