Quantum Hydrodynamics of Neutron Stars

Neutron stars (NSs), with average densities above that of the atomic nucleus, are cosmic laboratories with which to study matter at densities unattainable in terrestrial laboratories. The properties and dynamics of these compact objects are striking manifestations of quantum mechanics on a macroscopic scale. The rotational dynamics of a NS are governed by the movement of the quantum vortices that thread the rotating neutron superfluid of the stellar interior. A research project at Montana State University will develop a description of quantum hydrodynamics in a NS, with the aim of explaining observations of glitches in the spin of these rotating neutron stars, and determining whether a the spin of a NS can undergo precession. The project will also include training of undergraduate students in research and support public talks about neutron stars and this research at Bozeman’s Museum of the Rockies and other venues. This project will draw together the microscopic features of vortex motion into a global model of observed NS spin anomalies – spin glitches and spin precession. With numerical simulations, the research team will assess the consequences of a slip-stick, hysteretic character of vortex motion that was discovered in preliminary work by the group. The group will study how stellar spin down drives the vortex array into complex configurations as vortices twist, tangle, and get ejected from the star. A thermo-rotational instability could occur, wherein heat generated by vortex motion enhances the vortex mobility, creating a runaway and driving an observable spin event. They will develop a detailed model of how failure of the NS crust under spin-down or magnetic stresses liberates a large fraction of pinned vortices, producing a spin glitch. They will study if the motion of pinned vortices under thermal activation, in both the NS inner crust and core, could be compatible with observational evidence for long-period precession of the NS crust in Her X-1 and in magnetars. This project will be a synthesis of theoretical study of fundamental physical processes and directly testable predictions that will constrain the physical processes responsible for observed spin anomalies in NSs. This project will elucidate fundamental physical processes in NSs, advance the theoretical basis for interpreting and understanding observations, and further our understanding of dense matter and of nuclear interactions. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.