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Thermal origin of neutron star magnetic fields

Blandford, R. D. and Applegate, J. H. and Hernquist, L. (1983) Thermal origin of neutron star magnetic fields. Monthly Notices of the Royal Astronomical Society, 204 (4). pp. 1025-1048. ISSN 0035-8711. doi:10.1093/mnras/204.4.1025.

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It is proposed that magnetic field arises naturally in neutron stars as a consequence of thermal effects occurring in their outer crusts. The heat flux through the crust, which is carried mainly by degenerate electrons, can give rise to a possible thermoelectric instability in the solid crust which causes horizontal magnetic field components to grow exponentially with time. However, in order for the thermally driven growth to exceed ohmic decay, either the electron collision time must exceed existing estimates by a factor ∼ 3 or the surface layers comprise helium. A second instability is possible if the liquid phase that lies above the solid crust also contains a horizontal magnetic field. The heat flux will drive circulation which should amplify the field strength provided that there is a seed field in excess of ∼ 10^8 G. If either of these two instabilities develops the field will quickly grow to a strength of ∼ 10^(12) G, where the instabilities become non-linear. Further growth will saturate when either the magnetic stress exceeds the lattice yield stress or the temperature perturbations become non-linear, both of which occur at a subsurface field strength of ∼ 10^(14) G; the corresponding surface field strength is ∼ 10^(12) G. Further evolution of the magnetic field should lead to long-range order and yield neutron star magnetic dipole moments ∼ 10^(30) G cm^3, comparable with those observed. Newly-formed neutron stars should be able to develop their dipole moments in a hundred thousand years and maintain them for as long as heat flows through the crust. Thereafter, the dipole moment should decay in several million years, as observed in the case of most radio pulsars. Neutron stars that are formed spinning rapidly, like that in the Crab Nebula, should be able to grow magnetic fields far more rapidly since their rotational energy can also be tapped to drive thermoelectric currents. The interiors of neutron stars in binary systems may be heated by the energy released by accreting matter. The resulting heat flux may cause the production of magnetic fields in these objects. Binary pulsars, with their unusually low and persistent fields, have probably passed through this phase.

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Blandford, R. D.0000-0002-1854-5506
Hernquist, L.0000-0001-6950-1629
Additional Information:© 1983 Royal Astronomical Society. Provided by the NASA Astrophysics Data System. Received 1982 December 7; in original form 19'82 September 22. We thank the staff of NORDITA, where this work was initiated, for hospitality and especially Drs Gudmundsson and Pethick for guidance and encouragement. We thank Tom Hagstrom for assistance with the numerical computations. RB thanks the Director of the Institute for Theoretical Physics for hospitality during the completion of this paper and participants in the Space and Astrophysics Program for valuable comments. This research was supported by the National Science Foundation under grants AST80-17752 and PHY27-27084 and the Alfred P. Sloan Foundation. JHA acknowledges the support of a Bantrell Fellowship at Caltech.
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Alfred P. Sloan FoundationUNSPECIFIED
Caltech Bantrell FellowshipUNSPECIFIED
Issue or Number:4
Record Number:CaltechAUTHORS:20190521-165453098
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Official Citation:R. D. Blandford, J. H. Applegate, L. Hernquist, Thermal origin of neutron star magnetic fields, Monthly Notices of the Royal Astronomical Society, Volume 204, Issue 4, 1 October 1983, Pages 1025–1048,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95663
Deposited By: George Porter
Deposited On:23 May 2019 15:20
Last Modified:16 Nov 2021 17:14

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