Abstract
Gravitational radiation is a fundamental prediction of General Relativity. Elliptically deformed pulsars are among the possible sources emitting gravitational waves (GWs) with a strain-amplitude dependent upon the star's quadrupole moment, rotational frequency, and distance from the detector. We show that the gravitational wave strain amplitude h0 depends strongly on the equation of state of neutron-rich stellar matter. Applying an equation of state with symmetry energy constrained by recent nuclear laboratory data, we set an upper limit on the strain-amplitude of GWs produced by elliptically deformed pulsars. Depending on details of the EOS, for several millisecond pulsars at distances 0.18 kpc to 0.35 kpc from Earth, the maximalh0 is found to be in the range of ∼[0.4–1.5]×10−24. This prediction serves as the first direct nuclear constraint on the gravitational radiation. Its implications are discussed.
Highlights
Gravitational radiation is a fundamental prediction of General Relativity
Several mechanisms leading to such an asymmetry have been studied in literature: (1) Since the neutron star crust is solid, its shape might not be necessarily symmetric, as it would be for a fluid, with asymmetries supported by anisotropic stress built up during the crystallization period of the crust [6]. (2) due to its violent formation or due to its environment, the rotational axis may not coincide with a principal axis of the moment of inertia of the neutron star which make the star precess [7]
Even if the star remains perfectly symmetric about the rotational axis, since it precesses, it emits gravitational waves [7,8]. (3) the extreme magnetic fields presented in a neutron star cause magnetic pressure (Lorenz forces exerted on conducting matter) which can distort the star if the magnetic axis is not aligned with the axis of rotation [9], which is widely supposed to occur in order to explain the pulsar phenomenon
Summary
Gravitational radiation is a fundamental prediction of General Relativity. Elliptically deformed pulsars are among the possible sources emitting gravitational waves (GWs) with a strain-amplitude dependent upon the star’s quadrupole moment, rotational frequency, and distance from the detector. Gravitational wave strain amplitude depends on the degree to which the neutron star is deformed from axial symmetry which, in turn, is dependent upon the equation of state (EOS) of neutron-rich stellar matter.
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