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General Relativity and Quantum Cosmology, gr-qc,Astrophysics, Cosmology and Extragalactic Astrophysics, astro-ph.CO
Abstract:
The background of gravitational waves produced by the ensemble of rotating
neutron stars (which includes pulsars, magnetars and gravitars) is
investigated. A formula for \Omega(f) (commonly used to quantify the
background) is derived, properly taking into account the time evolution of the
systems since their formation until the present day. Moreover, the formula
allows one to distinguish the different parts of the background: the
unresolvable (which forms a stochastic background) and the resolvable. Several
estimations of the background are obtained, for different assumptions on the
parameters that characterize neutron stars and their population. In particular,
different initial spin period distributions lead to very different results. For
one of the models, with slow initial spins, the detection of the background can
be rejected. However, other models do predict the detection of the background
by the future ground-based gravitational wave detector ET. A robust upper limit
for the background of rotating neutron stars is obtained; it does not exceed
the detection threshold of two cross-correlated Advanced LIGO interferometers.
If gravitars exist and constitute more than a few percent of the neutron star
population, then they produce an unresolvable background that could be detected
by ET. Under the most reasonable assumptions on the parameters characterizing a
neutron star, the background is too faint. Previous papers have suggested
neutron star models in which large magnetic fields (like the ones that
characterize magnetars) induce big deformations in the star, which produce a
stronger emission of gravitational radiation. Considering the most optimistic
(in terms of the detection of gravitational waves) of these models, an upper
limit for the background produced by magnetars is obtained; it could be
detected by ET, but not by BBO or DECIGO.
