WoU-MMA: Generation of Ultrastrong Magnetic Fields in Nascent Neutron Stars

Neutron stars (NS), one end product of massive star evolution, are among the densest objects in the universe. Many NS show evidence of extremely strong magnetic fields that can be generated during their birth or in mergers of NS binaries. A theoretical investigation at Columbia University aims to understand the origin of ultrastrong magnetic fields and the diffusive processes that regulate the onset of turbulence and magnetic field generation. Numerical experiments will be carried out in the relevant physical regime. The proposed systematic revision of dynamo mechanisms can have a significant impact on the field and pave the way for realistic magnetohydrodynamic simulations of collapsing stars and mergers. In addition, public outreach efforts will be undertaken to present the research in a more accessible form to larger audiences, including high-school students at two existing educational programs. The project will involve training of university students and postdoctoral researchers. The research team will investigate mechanisms generating ultra-strong large-scale magnetic fields in magnetars and NS mergers. A turbulent dynamo inside a nascent rotating NS requires an instability to create turbulence, and the canonical candidates include the Tayler instability and convection. The proposed research has two parts: (1) A crucial revision of the linear stability analysis to correctly capture the interplay of rotation and microscopic diffusive processes (in particular, viscosity and thermal conductivity due to neutrino diffusion). Preliminary results suggest a new picture of marginally stable proto-neutron stars, potentially explaining two classes: ordinary pulsars and magnetars. A similar analysis of mergers will give necessary conditions for a successful dynamo in the merger remnants. (2) State-of-the-art simulations of nonlinear turbulence triggered in nascent remnants. The simulations will model a rotating, stratified, magnetized fluid sphere using a pseudo-spectral code. They will allow direct control of diffusivities and implementation of the correct physical regime of turbulence development. The numerical tools will also be used to investigate a very different origin of magnetic fields: the chiral magnetic effect.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.