Superfluid Dynamics in Neutron Stars
The interior of a neutron star is believed to exist in a superfluid state. The superfluid is threaded by quantized vortices which interact with each other and with the crust of the star. In this project, we investigate the flow dynamics of the superfluid numerically, using a state-of-the-art spectral code, in order to identify the conditions under which the flow is turbulent and/or unstable. The aim is to model the mysterious rotational irregularities (glitches, timing noise) seen in radio timing observations of pulsating neutron stars (pulsars).
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Principal Investigator Andrew MelatosAstrophysics Group, School of Physics University of Melbourne |
Project f68 |
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Co-Investigators Carlos PeraltaAstrophysics Group, School of Physics University of Melbourne |
RFCD Codes 240101, 240204 |
Significant Achievements, Anticipated Outcomes and Future Work
We are on track to produce the first large-scale simulations describing the global pattern of superfluid flow inside a neutron star. The simulations solve the HVBK equations of motion for a mixture of normal fluid and superfluid given a variety of phenomenological forms for the mutual friction and tension forces, under a range of physical conditions. In 2003, we achieved the following milestones, in collaboration with Dr Ooi and his group from the Dept of Mech. Eng. at U. Melbourne.
1. We modified an existing, one-fluid, Navier-Stokes code to accommodate accelerating boundary conditions, in preparation for our neutron star studies, where the stellar crust does not rotate at constant speed.
2. We applied the code in this form to study the stability of spherical Taylor-Couette flow for a range of Reynolds numbers and shell thicknesses. Our results will form the basis of a systematic study of this system, to be completed and published in 2004.
3. We extended the code to simulate two fluids, one viscous and the other inviscid. This extension has just been tested successfully with an idealised, linear coupling between the two fluids.
4. We are adding more realistic coupling terms to the extended code and will apply the code to the problem of rotational irregularities in neutron stars in 2004.
Computational Techniques Used
The code is built around a proprietary Navier-Stokes solver developed by Dr Ooi and his group at U. Melbourne and their international collaborators. The solver is based on a Chebyshev spectral algorithm. It is not parallelized in MPI. However, the applications we are pursuing require grids of hundreds of runs with different initial conditions (to delineate the basins of instability in the physical system). The project would therefore be impossible without the extensive multi-processor facilities provided by VPAC and the APAC National Facility.
Publications, Awards and External Funding
External Funding and Awards
Melatos is closely involved in the theory component of the Astronomy Virtual Observatory program in Australia through his collaborations with Webster (UMelb), Barnes (UMelb), and Maddison (Swin). This program is funded externally through LIEF and supported by VPAC/APAC. It is indirectly related to project f68.
Publications
The papers below are indirectly related to project f68.
D. J. B. Payne, A. Melatos, Burial of the polar magnetic field of an accreting neutron stars. I. Self-consistent analytic and numerical equilibria, MNRAS, 2004, in press
D. J. B. Payne, A. Melatos, E. S. Phinney, Gravitational waves from an accreting neutron star with a magnetic mountain, AIP Conf. Proc., 686, 2003, 92-98.