Spin-down induced quark-hadron phase transition in cold isolated neutron stars

We have studied the spin-down induced phase transition (PT) in cold, isolated neutron stars in this work. After birth, as the star slows down, its central density rises and crosses the critical density of PT, and a quark core is seeded inside the star. Intermediate-mass stars are more likely to have a quark seeding in their lifetime at birth. Smaller neutron stars do not have a quark core and remain neutron stars throughout their life, whereas in massive stars, a quark core exists at their centre from birth. In intermediate and massive stars, the quark core grows further as the star slows down. The appearance of a quark core leads to a sudden change in the moment of inertia of the star in its evolutionary history, and is also reflected in a sudden discontinuity in the braking index of the star (at the frequency where the quark core first seeds). The energy released during the PT process as the quark core is seeded can excite the f-mode oscillation in the star and is emitted in the form of the gravitational wave, which is in the range of detection with present operating detectors; however, future detectors will enable a more clean extraction of this signals. Also, neutrinos and bursts of gamma-rays can originate from PT events. The spin-down induced PT could be gradual or in the form of subsequent leaps producing persistent or multiple transient emissions.