Gravitational wave signature from phase transition of a combusting neutron star to quark star

Abstract

ABSTRACT Fluctuation at the neutron star centre gives rise to a small deconfined quark core very close to the star centre. The density discontinuity at the quark–hadron boundary initiates a shock wave, which propagates outwards of the star. The shock has enough energy to combust nuclear matter to 2-flavour quark matter in the star. The 2-flavour quark matter is not stable and settles to a stable 3-flavour matter in the weakly interacting time-scale. In this paper, we study the conversion of 2-flavour matter to 3-flavour matter. We set-up a differential equation to convert the excess of down quarks to strange quarks involving weak reaction and diffusion of quarks. Calculating the reaction rate and diffusion, we solve the differential equation to find the velocity of the conversion front. As the conversion front moves out, the density profile changes, bringing about a change in the star’s quadrupole moment and thereby emitting gravitational waves (GWs). As the conversion process occurs, the temperature of the star rises, but the neutrino carries away the heat in some tens of ms. The GW amplitude of a colder star is well within the present detector capability, but the frequency is slightly on the higher side. Relatively hotter stars are on the boundary of present detectors and easily detectable with future detectors, and their frequency is also within the present detectability range. In comparison, phase transition from Galactic pulsars is easily detectable with present detectors.