Speaker
Description
A neutron star is expected to contain a rotating neutron superfluid, threaded by 10^17 quantized vortices, in an environment with a much larger number of pinning sites. The interaction between these two entities, along with the spin-down of the star's crust, is thought to be the primary driver of pulsar glitches. Given reasonable computational resources, existing Gross-Pitaevskii simulations of this system can handle about 600 vortices. Meanwhile, hydrodynamic simulations can support up to 10^4 point vortices in 2D, but are often constrained by a limited set of pinning strengths. Here, we present a fast and robust simulation suite enabling the tracking of up to 10^5 vortices against a background of pinning sites having a wide range of strengths. We achieve this by adapting the Barnes-Hut algorithm to a well-established hydrodynamic prescription. Utilizing this setup to study the evolution of the pinned vortex array in a spinning-down neutron star, we find that the vortex array does not expand outward uniformly, as often expected. Instead, it spontaneously separates into macroscopic vortex-dense and vortex-scarce regions. This emergence of a geometric length-scale carries immediate relevance for the propagation of pulsar glitches. We conclude by demonstrating the flexibility of our modular suite by establishing a star with significant pinning inhomogeneities, such as those expected to result from crustquakes. We find that the small glitches in this case are staggered and carry an imprint of the underlying inhomogeneity.