[Paper Review] Pulsar glitches from quantum vortex networks

Giacomo Marmorini, Shigehiro Yasui+1 more|arXiv (Cornell University)|Oct 18, 2020

Quantum, superfluid, helium dynamics4 citations

TL;DR

This paper proposes that pulsar glitches arise from quantum vortex networks at the interface between s-wave and p-wave superfluids in neutron star cores, where integer vortices in the s-wave region connect to half-quantized vortices in the p-wave region via boojum structures. The model naturally reproduces the observed scaling law P(E) ∼ E^−0.88 without free parameters, explaining glitches as collective unpinning events in a topological vortex network.

ABSTRACT

Neutron stars or pulsars are very rapidly rotating compact stars with extremely high density. One of the unsolved long-standing problems of these enigmatic celestial bodies is the origin of pulsars' glitches, i.e., the sudden rapid deceleration in the rotation speed of neutron stars. Although many glitch events have been reported, there is no consensus on the microscopic mechanism responsible for them. One of the important characterizations of the glitches is the scaling law $P(E) \sim E^{-α}$ of the probability distribution for a glitch with energy $E$. Here, we reanalyse the accumulated up-to-date observation data to obtain the exponent $α\approx 0.88$ for the scaling law, and propose a simple microscopic model that naturally deduces this scaling law without any free parameters. Our model explains the appearance of these glitches in terms of the presence of quantum vortex networks arising at the interface of two different kinds of superfluids in the core of neutron stars; a $p$-wave neutron superfluid in the inner core which interfaces with the $s$-wave neutron superfluid in the outer core, where each integer vortex in the $s$-wave superfluid connects to two half-quantized vortices in the $p$-wave superfluid through structures called "boojums."

Motivation & Objective

• To resolve the long-standing puzzle of pulsar glitches, which involve sudden spin-downs in rotating neutron stars.
• To explain the empirically observed scaling law P(E) ∼ E^−α for glitch energy distribution, with α ≈ 0.88 from updated observational data.
• To propose a microscopic mechanism rooted in quantum vortex networks and topological defects (boojums) at the interface of distinct superfluid phases.
• To demonstrate that the scaling law emerges naturally from the network structure without adjustable parameters.

Proposed method

• Model the neutron star core as a two-phase superfluid system: s-wave superfluid in the outer core and p-wave superfluid in the inner core.
• Describe vortices using Ginzburg-Landau-type order parameters: integer vortices (IQVs) in s-wave and half-quantized vortices (HQVs) in p-wave superfluids.
• Introduce boojums as topological defects at the s-wave/p-wave interface, enabling one IQV to connect to two HQVs.
• Construct a network of interconnected vortices where clusters of HQVs and IQVs form topologically stable configurations.
• Model glitch events as catastrophic unpinning of entire vortex clusters, where all vortices in a connected network release simultaneously.
• Use statistical mechanics of the vortex network to derive the probability distribution of glitch energies, leading to a power-law scaling.

Experimental results

Research questions

• RQ1 What microscopic mechanism can naturally explain the observed E^−0.88 scaling law for pulsar glitch energies?
• RQ2 How do quantum vortices in different superfluid phases (s-wave vs. p-wave) interact across an interface to produce collective glitch events?
• RQ3 Can the collective unpinning of vortex clusters in a topological network reproduce the observed power-law statistics of glitches?
• RQ4 What role do boojum defects play in mediating the connection between integer and half-quantized vortices in neutron star cores?
• RQ5 Is the observed scaling exponent α ≈ 0.88 consistent with a fundamental physical model of vortex network dynamics?

Key findings

• The analysis of up-to-date observational data yields a scaling exponent α ≈ 0.88 for the glitch energy distribution P(E) ∼ E^−α.
• The proposed vortex network model with boojum-mediated connections between IQVs and HQVs naturally produces the observed scaling law without any free parameters.
• The model explains glitches as collective unpinning events involving entire vortex clusters, not isolated vortices, resolving the contradiction with smooth spin-down.
• The p-wave superfluid in the inner core is topologically nontrivial, supporting Majorana fermions and enabling stable HQV configurations.
• The interface between s-wave and p-wave superfluids hosts a network of interconnected vortices, with boojums ensuring topological consistency of the vortex structure.
• The model is potentially testable in laboratory systems such as ultracold atomic gases or 3He superfluids with A-B phase boundaries.