Gravitational wave background from neutron star phase transition for a new class of equation of state

Abstract

Abstract. We study the generation of a stochastic gravitational wave (GW) background produced by a population of neutron stars (NSs) which go over a hadron-quark phase transition in its inner shells. We obtain, for example, that the NS phase transition, in cold dark matter scenarios, could generate a stochastic GW background with a maximum amplitude of hBG ∼ 10 −24 , in the frequency band ≃ 20 − 2000 Hz for stars forming at redshifts of up to z ≃ 20. We study the possibility of detection of this isotropic GW background by correlating signals of a pair of 'advanced' LIGO observatories. IntroductionIt is widely accepted that neutron stars (NSs) are born with fast rotating angular velocities. Due to magnetic torques, however, the NS periods could well be spun down. This spin-down causes a reduction in the centrifuge force and, consequently, the central energy density of the NSs increases. Those stars, born with densities close to that of the quark deconfinement, may undergo a phase transition forming a strange quark matter core. It is worth stressing, however, that it is not a common sense that such a transition really takes place.As a consequence of such a putative phase transition, the stars could suffer a collapse which could excite mechanical oscillations. The great amount of energy generated in this process, ∆E ∼ 10 53 ergs (∼ 0.1 M ⊙ c 2 ) [1], could be dissipated, at least partially, in the form of gravitational waves (GWs), which are studied in the present work.We adopted in the present paper the history of star formation derived by Springel & Hernquist [2], who employed hydrodynamic simulations of structure formation in a Λ cold dark matter (ΛCDM) cosmology. These authors study the history of cosmic star formation from the "dark ages", at redshift z ∼ 20, to the present.Besides the reliable history of star formation by Springel & Hernquist, we consider the role of the parameters α i=1,2 , which gives the fraction of the progenitor mass which forms the remnant NSs. We consider that the remnant mass is given as a function of the progenitor mass, namely M r = α 1 m + α 2 . Later on we justify why M r is written in this way. Recall that a given initial mass function (IMF) refers to the distribution function of the stellar progenitor mass, and also to the masses of the remnant compact objects left as a result of the stellar evolution.In the present study we have adopted a stellar generation with a Salpeter IMF, which is consistent with Springel & Hernquist, since they show that population II stars could have been formed at high redshift too. We then discuss briefly what conclusions would be drawn whether

Energy release from hadron-quark phase transition in neutron stars and the axialwmode of gravitational waves

“…To understand the mechanism of the hadron-quark phase transition and the associated energy release, their dependence on properties of the dense hadronic and quark matter, the way the energy release being dissipated in NSs or carried away by gravitational waves, and the gravitational wave signatures of the EOS of dense matter and the expected hadron-quark phase transition are among the many interesting questions currently under intense investigations in neutron star physics and gravitational wave astronomy, see, e.g., refs. [3,[6][7][8][9][10][11][12].…”