EDP Sciences
Free access
Volume 420, Number 2, June III 2004
Page(s) 631 - 645
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20034078

A&A 420, 631-645 (2004)
DOI: 10.1051/0004-6361:20034078

The occurrence of the Hall instability in crusts of isolated neutron stars

M. Rheinhardt1, D. Konenkov2 and U. Geppert1

1  Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
    e-mail: urme@aip.de
2  Ioffe Physico-Technical Institute, 194021 Af. F., Politechnicheskaya 26, St. Petersburg, Russia
    e-mail: dyk@astro.ioffe.rssi.ru

(Received 15 July 2003 / Accepted 2 March 2004)

In former papers we showed that during the decay of a neutron star's magnetic field under the influence of the Hall drift, an unstable growth of small-scale field structures at the expense of the large-scale background field may happen. This linear stability analysis was based on the assumption of a uniform density throughout the neutron star crust, whereas in reality the density and all transport coefficients vary by many orders of magnitude. Here, we extend the investigation of the Hall drift induced instability by considering realistic profiles of density and chemical composition, as well as background fields with more justified radial profiles. Two neutron star models are considered differing primarily in the assumption on the core matter equation of state. For their cooling history and radial profiles of density and composition we use known results to infer the conductivity profiles. These were fed into linear calculations of a dipolar field decay starting from various initial configurations. At different stages of the decay, snapshots of the magnetic fields at the equator were taken to yield background field profiles for the stability analysis. Its main result is that the Hall instability may really occur in neutron star crusts. Characteristic growth times are in the order of  $\la$ $10^4\ldots10^6$ yrs depending on cooling age and background field strength. The influence of the equation of state and of the initial field configuration is discussed.

Key words: stars: neutron -- stars: magnetic fields

Offprint request: M. Rheinhardt, mreinhardt@aip.de

© ESO 2004