Phase transitions in neutron stars and gravitational wave emission

Abstract

We review the detectability of gravitational waves generated by oscillations excited during a phase transition from hadronic matter to deconfined quark-gluon matter in the core of a neutron star. Neutron star properties were computed using a Boguta and Bodmer's based model and the MIT bag model. The maximum energy available to excite mechanical oscillations into the star is estimated by energy difference between the configurations with and without a quark-gluon matter core. On basis of the planned sensitivity of present laser interferometers (VIRGO or LIGO I) and those of the next generation (LIGO II), the maximum volume to be probed by these experiments is determined. These results are used as an indication of the potential detectability of neutron stars as sources of gravitational waves. Our results indicate that the maximum distance probed by the detectors of the first generation is well beyond M31, whereas the second generation detectors will probably see phase transition events at distances two times longer, but certainly not yet attaining the Virgo cluster.

Possible sources of gravitational wave bursts detectable today

“…(43) we find that a signal E s ≃ 100 mK can be obtained from a particle which crosses the bar longitudinally, with an energy loss in Aluminium dE dx ≃ 20 GeV cm (46) or, in a generic material,…”

“…For a NS spinning with P rot of the order of a few ms, τ GW is smaller than the damping time due to viscosity, and the energy liberated will be radiated away mainly in GWs (see also refs. [45,46]). …”

“…In particular, the core of a NS can perform a phase transition from a hadronic to a deconfined quark-gluon phase. In the literature [45,46] it has been considered the possibility that an accreting NS acquires a sufficient mass to perform completely the transition from a hadronic core to a quark-gluon core. The energy gained in the transition, for a NS with a mass M ∼ 1.5M ⊙ , is of order 0.15M ⊙ c 2 [46], and it has been observed that this large energy can excite quasi normal modes and be liberated in a GW bursts (with high efficiency if the NS rotates sufficiently fast).…”

“…In the literature [45,46] it has been considered the possibility that an accreting NS acquires a sufficient mass to perform completely the transition from a hadronic core to a quark-gluon core. The energy gained in the transition, for a NS with a mass M ∼ 1.5M ⊙ , is of order 0.15M ⊙ c 2 [46], and it has been observed that this large energy can excite quasi normal modes and be liberated in a GW bursts (with high efficiency if the NS rotates sufficiently fast). Particularly interesting appear the discontinuity g-modes [52], having typical frequency in the range 0.5-1.4 kHz and constituting an unique probe for density discontinuities, like the ones induced by phase transitions.…”

Constraining crystalline color superconducting quark matter with gravitational-wave data

“…In this paper, we show that the observational upper limits on gravitational-wave emission from known pul- * Electronic address: lmlin@phy.cuhk.edu.hk sars can be used to constrain compact star models composed of crystalline color superconducting quark matter. The prospect of detecting the gravitational-wave signals emitted by quark stars has been considered before (e.g., [12,13,14,15,16]). However, our work represents the first attempt to make use of real observational data to set constraint on theoretical parameters of the quark matter.…”