Gravitational Waves from Neutron Stars with Large Toroidal B-fields

By C. Cutler. 2002

253 citations recorded by the source corpus.

We show that NS's with large toroidal B fields tend naturally to evolve into potent gravitational-wave (GW) emitters. The toroidal field ${B}_{t}$ tends to distort the NS into a prolate shape, and this magnetic distortion dominates over the oblateness ``frozen into'' the NS crust for ${B}_{t}\ensuremath{\gtrsim}3.4\ifmmode\times\else\texttimes\fi{}{10}^{12}\mathrm{G}({\ensuremath{\nu}}_{s}/300\mathrm{Hz}{)}^{2}.$ An elastic NS with frozen-in B field of this magnitude is clearly secularly unstable: the wobble angle between the NS's angular momentum ${J}^{i}$ and the star's magnetic axis ${n}_{B}^{i}$ grows on a dissipation time scale until ${J}^{i}$ and ${n}_{B}^{i}$ are orthogonal. This final orientation is clearly the optimal one for GW emission. The basic cause of the instability is quite general, so we conjecture that the same final state is reached for a realistic NS, with superfluid core. Assuming this, we show that for LMXB's with ${B}_{t}\ensuremath{\sim}2\ifmmode\times\else\texttimes\fi{}{10}^{12}\ensuremath{-}2\ifmmode\times\else\texttimes\fi{}{10}^{14}\mathrm{G},$ the spindown from GW's is sufficient to balance the accretion torque---supporting a suggestion by Bildsten. The spindown rates of most millisecond pulsars can also be attributed to GW emission sourced by toroidal B fields, and both these sources could be observed by LIGO II. While the first-year spindown of a newborn NS is most likely dominated by electromagnetic processes, reasonable values of ${B}_{t}$ and the (external) dipolar field ${B}_{d}$ can lead to detectable levels of GW emission, for a newborn NS in our own Galaxy.

Subfields: Astronomy and Astrophysics, Geophysics, Ocean Engineering

View Paper: https://www.semanticscholar.org/paper/8ab18fe91a6c84c146096bfa216837180a180220

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Citations in the corpus

Gravitational Radiation from an Accreting Millisecond Pulsar with a Magnetically Confined Mountain (2005, background): “…as a possible exception (Konno et al. 2000; Ioka 2001; Palomba 2001), as are objects whose internal toroidal fields are many times greater than B (Cutler 2002) or whose macroscopically averaged Maxwell stress tensors are enhanced relative to uniform magnetization because the internal field is…”
Physics, Astrophysics and Cosmology with Gravitational Waves (2009, background): “One mechanism, proposed by Cutler [127], is that a large buried toroidal magnetic field could, by pulling in the waist of a spinning star, turn it into a prolate spheroid.”
The astrophysical gravitational wave stochastic background (2011, background): “On the other hand, It has been suggested that the spindown could become purely gravitational if the internal magnetic field could is dominated by a very strong toroidal component (Cutler 2002; Stella et al. 2005), of the order of 1016 G).”
The basics of gravitational wave theory (2005, background): “Examples of some interesting mechanisms include misalignment of a star’s internal magnetic field with the rotation axis [77] and distortion by accreting material from a companion star [78, 79] (discussed in more detail below).”
Detecting gravitational wave emission from the known accreting neutron stars (2008, background): “…1998; Ushomirsky, Cutler & Bildsten 2000; Melatos & Payne 2005; Payne & Melatos 2006; Haskell, Jones & Andersson 2006), magnetic deformation (Cutler 2002; Haskell et al. 2008) or internal r-mode oscillations (Bildsten 1998; Andersson, Kokkotas & Stergioulas 1999; Levin 1999; Andersson et…”
Modelling magnetically deformed neutron stars (2007, background): “As a sanity check of this result we can compare to the estimate used by Cutler (2002).”
The Proto-Magnetar Model for Gamma-Ray Bursts (2010, background): “In equation (3) we neglect angular momentum losses due to gravitational waves, which become important if the NS is sufficiently aspherically distorted by its strong interior magnetic field (e.g. Cutler 2002; Arons 2003; Stella et al. 2005; Dall’Osso et al. 2009).”