Journal Article

Low-<i>T</i>/|<i>W</i>| instabilities in differentially rotating protoneutron stars with magnetic fields

Wen Fu and Dong Lai

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 413, issue 3, pages 2207-2217
Published in print May 2011 | ISSN: 0035-8711
Published online May 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.18296.x
Low-T/|W| instabilities in differentially rotating protoneutron stars with magnetic fields

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Recent hydrodynamical simulations have shown that differentially rotating neutron stars formed in core-collapse supernovae may develop global non-axisymmetric instabilities even when T/|W| (the ratio of the rotational kinetic energy T to the gravitational potential energy |W|) is relatively small (less than 0.1). Such low-T/|W| instability can give rise to efficient gravitational wave emission from the protoneutron star. We investigate how this instability is affected by magnetic fields using a cylindrical stellar model. Wave absorption at the corotation resonance plays an important role in facilitating the hydrodynamic low-T/|W| instability. In the presence of a toroidal magnetic field, the corotation resonance is split into two magnetic resonances where wave absorptions take place. We show that the toroidal magnetic field suppresses the low-T/|W| instability when the total magnetic energy, WB, is of the order of 0.2 T or larger, corresponding to toroidal fields of a few ×1016 G or stronger. Although poloidal magnetic fields do not influence the instability directly, they can affect the instability by generating toroidal fields through linear winding of the initial poloidal field and magnetorotational instability. We show that an initial poloidal field with strength as small as 1014 G may suppress the low-T/|W| instability.

Keywords: gravitational waves; hydrodynamics; instabilities; MHD; stars: neutron; stars: rotation

Journal Article.  4633 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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