| Abstract : | The existence of quark stars is an open problem in astrophysics, and the quest to find such stars has attained a lot of focus in recent years. According to a conjecture of QCD, at extreme densities found in neutron star interior, the normal nuclear matter is no longer the stable ground state, and it is prone to convert to 3-flavor quark matter (u, d, s quark matter), which is the ground state at such densities. We addressed the shock-induced phase transition scenario by performing simulations in general relativistic hydrodynamics code (GR1D). The simulation reveals the conversion time to be 30-50 microseconds, which indicates a rapid process. This time scale differs from previous studies involving simple analytical estimates. The obtained gravitational wave signal is short-lived (burst-type) with a frequency of about 100 kilohertz and may be observed in future high-frequency GW detectors. The aftermath of deconfinement is 2-flavor quark matter (u,d) to 3-flavor quark matter (u,d,s) conversion and distinct emissions can originate from it. The time scale and energy budget available indicate that short gamma-ray bursts and fast radio bursts could arise in phase transition events. Further, we have addressed the spin-down driven phase transition scenario, wherein magnetic braking drives neutron stars from their birth (Keplerian rotation) to later stages of life (slow spin). The density rise during spin-down can lead to the formation of a quark core or the growth of an existing quark core (from birth). Such progressive phase transitions differ from catastrophic ones and can produce persistent or multiple transient signals (braking index changes, GWs from excited oscillation modes, neutrino bursts). Detecting these multi-messenger signals and their sky localization may help find the quark/hybrid stars formed via phase transition. |
