Abstract
A framework is presented for a statistical theory of neutron star glitches, motivated by the results emerging from recent Gross–Pitaevskii simulations of pinned, decelerating quantum condensates. It is shown that the observed glitch size distributions cannot be reproduced if superfluid vortices unpin independently via a Poisson process; the central limit theorem yields a narrow Gaussian for the size distribution, instead of the broad, power-law tail observed. This conclusion is not altered fundamentally when a range of pinning potentials is included, which leads to excavation of the potential distribution of occupied sites, vortex accumulation at strong pinning sites, and hence the occasional, abnormally large glitch. Knock-on processes are therefore needed to make the unpinning rate of a vortex conditional on the pinning state of its near and/or remote neighbours, so that the Gaussian size distributions resulting generically from the central limit theorem are avoided. At least two knock-on processes, nearest-neighbour proximity knock-on and remote acoustic knock-on, are clearly evident in the Gross–Pitaevskii simulation output. It is shown that scale-invariant (i.e. power-law) vortex avalanches occur when knock-on is included, provided that two specific relations hold between the temperature and spin-down torque. This fine-tuning is unlikely in an astronomical setting, leaving the overall problem partly unsolved. A state-dependent Poisson formalism is presented which will form the basis of future studies in this area.
Highlights
Pulsar glitches — the discrete, randomly-timed jumps in the spin frequency of a pulsar — are characterised by powerlaw size and exponential waiting-time distributions (Wong et al 2001; Melatos et al 2008)
New physics needs to be added to the vortex unpinning paradigm in order to understand: (1) why some pulsars glitch and others do not; (2) why glitch sizes span up to four decades in an individual pulsar; (3) why there are large glitches involving the simultaneous unpinning of ∼ 1012 vortices, rather than a steady trickle of unpinning events; (4) why vortices skip over ∼ 109 pinning sites before repinning; (5) if large-scale inhomogeneities develop in a vortex lattice pinned to a homogeneous pinning array; and (6) how waiting times between glitches can be deduced endogenously from a model based on individual vortex unpinning
Our model addresses many of these questions by incorporating the following three novel features: (1) individual vortices unpin explicitly according to a Poisson process whose rate is governed by the global superfluid-crust shear; (2) there is a range of available pinning energies, representing the myriad imperfections in the pulsar crustal lattice; and (3) unpinned vortices catalyse knock-on unpinnings at neighbouring pinning sites, which we model as a branching process
Summary
Pulsar glitches — the discrete, randomly-timed jumps in the spin frequency of a pulsar — are characterised by powerlaw size and exponential waiting-time distributions (Wong et al 2001; Melatos et al 2008) These statistics point to an underlying collective process, similar to other complex systems such as neural and social networks (Worrell et al 2002), soil moisture balance (Porporato et al 2004; Daly & Porporato 2007), electricity grids (Carreras et al 2002), forest fires (Turcotte 1999), earthquakes (Drossel 1996) and many more (Goss et al 1989; Schonfisch & de Roos 1999; Cornforth et al 2005; Boerlijst & Hogeweg 1991; Suki et al 1994; Wu et al 2010).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
