Global Three‐dimensional Flow of a Neutron Superfluid in a Spherical Shell in a Neutron Star

Peralta, C.; Melatos, A.; Giacobello, Matteo; Ooi, Andrew

doi:10.1086/497899

Cited by 75 publications

(141 citation statements)

References 79 publications

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“…Finally, a further coarse-graining of our model would correspond to theories of the HallVinen (Hall & Vinen 1956) and Bekharevich-Khalatnikov (Leggett 2006) type, i.e. to statistical theories of thermal superfluid turbulence (Henderson & Barenghi 2004;Peralta et al 2005Peralta et al , 2006Peralta et al , 2008Andersson, Sidery & Comer 2007;Sidery, Andersson & Comer 2008;Melatos & Peralta 2010). The mathematical difficulties involved in this coarse-graining are great, and our results could guide the relevant analyses.…”

Section: Introductionmentioning

confidence: 85%

Spreading of superfluid vorticity clouds in normal-fluid turbulence

Kivotides

2010

J. Fluid Mech.

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In this paper, we formulate a self-consistent model of thermal superfluid dynamics. By solving it, we analyse the problem of superfluid vorticity cloud propagation in normal-fluid turbulence. We show that superfluid cloud expansion is driven by pattern-forming superfluid vortex instabilities taking place in the interface layer between the cloud's bulk and the outer undisturbed normal-fluid turbulence. The radius of the cloud increases linearly with time. Mutual friction transfers energy from the normal-fluid turbulence to the superfluid cloud, whilst damping the smallest normal-fluid turbulence motions. This damping action is much weaker than viscous dissipation effects in a corresponding pure normal-fluid turbulence. The energy spectrum of superfluid turbulence presents the k −3 scaling that characterizes the spiral superfluid vorticity patterns of normal vortex tube-superfluid vortex interactions. The corresponding k −2 pressure spectrum signifies the singular nature of superfluid vorticity. These two scalings coincide in wavenumber space with the Kolmogorov regime in the normal-fluid turbulence. We compute a fractal dimension d f ≈ 1.652 for superfluid vorticity. Due to simpler underlying superfluid vortex dynamics in relation to the strongly nonlinear classical vortex dynamics, this fractal dimension is smaller than the corresponding dimension of vortex tube centrelines in classical turbulence.

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Section: Introductionmentioning

confidence: 85%

Spreading of superfluid vorticity clouds in normal-fluid turbulence

Kivotides

2010

J. Fluid Mech.

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“…Peralta et al [28,177] showed that, in the absence of magnetic fields, a sizeable axial counterflow develops which exceeds the threshold for the Donnelly-Glaberson instability in most of the star. The mutual friction force changes form and strength in those regions where the threshold is exceeded.…”

Section: Hydrodynamical Instabilitesmentioning

confidence: 99%

Models of pulsar glitches

Haskell

Melatos

2015

Int. J. Mod. Phys. D

318

304

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Radio pulsars provide us with some of the most stable clocks in the universe. Nevertheless several pulsars exhibit sudden spin-up events, known as glitches. More than forty years after their first discovery, the exact origin of these phenomena is still open to debate. It is generally thought that they an observational manifestation of a superfluid component in the stellar interior and provide an insight into the dynamics of matter at extreme densities. In recent years there have been several advances on both the theoretical and observational side, that have provided significant steps forward in our understanding of neutron star interior dynamics and possible glitch mechanisms. In this article we review the main glitch models that have been proposed and discuss our understanding, in the light of current observations.Radio pulsars are thought to be rotating magnetised neutron stars (NS). The huge moment of inertia (of the order of 10 45 g cm 2 ) leads to exceptionally stable rotation rates and provides us with some of the most precise clocks in the universe. The best timed millisecond pulsars are stable to a precision which rivals that of atomic clocks [1]. Nevertheless radio pulsars exhibit several timing irregularities, the most striking of which are the so-called glitches. While most objects are observed to steadily spin-down due to the emission of electromagnetic and, possibly, gravitational waves, many pulsars show sudden increases in their spin, in some cases followed by an increase in their spin-down rate, i.e. glitches. Most pulsars also show slower, long-term, stochastic deviations from a regular spin-down law, that are generally classed as 'timing noise' and are not the main focus of this review article.Soon after the discovery of the first glitches in the Vela [2,3] and Crab [4,5] pulsars in 1969, several mechanisms were suggested to explain these phenomena. Although some initial suggestions featured external mechanisms, such as plasma explosions in the magnetosphere [6] or planets around the pulsar [7], the lack of radiative and pulse profile changes associated with these events was taken as evidence for an internal origin. The situation is different for rotating radio transients (RRATs) and magnetars, which are now known to glitch and do exhibit, amongst other peculiar traits, radiative changes associated with these events [8][9][10][11]. Magnetospheric activity is likely to play a role in these objects, as we discuss below.There are two main internal glitch mechanisms that have been examined in the literature. The first set of models relies on the fact that the outer layers of a neutron star form a crystalline crust that can support stress. As the NS spins down, the liquid core adjusts its shape to the rotation rate, while the solid crust maintains the shape appropriate for the previous, higher, spin rate. This leads to an increasing amount of strain building up in the crust, which is eventually released in the form of a star quake. The quake causes a sudden rearrangement of the moment of inertia and...

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“…The force per unit length should then be calculated as an average over all angular directions. In following this procedure we neglect the effects of turbulence, which may arise in NS interiors (Peralta 2005;Peralta et al 2006;Andersson, Sidery & Comer 2007), possibly due to modes of oscillations of the superfluid that may be unstable in the presence of pinning (Glampedakis & Andersson 2009;Link 2012). In this case the vortex array is likely to form a complex tangle, that must, however, still be polarized due to the rotation of the star.…”

Section: Mesoscopic Pinning Forcementioning

confidence: 99%

Mesoscopic pinning forces in neutron star crusts

Seveso¹,

Pizzochero²,

Grill³

et al. 2015

Mon. Not. R. Astron. Soc.

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The crust of a neutron star is thought to be comprised of a lattice of nuclei immersed in a sea of free electrons and neutrons. As the neutrons are superfluid their angular momentum is carried by an array of quantized vortices. These vortices can pin to the nuclear lattice and prevent the neutron superfluid from spinning down, allowing it to store angular momentum which can then be released catastrophically, giving rise to a pulsar glitch. A crucial ingredient for this model is the maximum pinning force that the lattice can exert on the vortices, as this allows us to estimate the angular momentum that can be exchanged during a glitch. In this paper we perform, for the first time, a detailed and quantitative calculation of the pinning force per unit length acting on a vortex immersed in the crust and resulting from the mesoscopic vortexlattice interaction. We consider realistic vortex tensions, allow for displacement of the nuclei and average over all possible orientation of the crystal with respect to the vortex. We find that, as expected, the mesoscopic pinning force becomes weaker for longer vortices and is generally much smaller than previous estimates, based on vortices aligned with the crystal. Nevertheless the forces we obtain still have maximum values of order f pin ≈ 10 15 dyn/cm, which would still allow for enough angular momentum to be stored in the crust to explain large Vela glitches, if part of the star is decoupled during the event.

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Global Three‐dimensional Flow of a Neutron Superfluid in a Spherical Shell in a Neutron Star

Cited by 75 publications

References 79 publications

Spreading of superfluid vorticity clouds in normal-fluid turbulence

Spreading of superfluid vorticity clouds in normal-fluid turbulence

Models of pulsar glitches

Mesoscopic pinning forces in neutron star crusts

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