If the baryonic mass of a neutron star (NS) is high enough, the pressure and the energy density in the central region may attain such values that a phase transition in its core is possible. In such a case the star develops a quark core. However, if the star is in rapid rotation, the central pressure and energy density are below the critical values, and the NS has an internal structure constituted essentially by hadrons. If as expected the NS has a magnetic field, the rotation velocity will decrease due to the canonical magnetic dipole breaking mechanism. Therefore, after a certain time, phase transition conditions again might be reached.
Thus, as during its evolution the rotation frequency of pulsars decreases due to magnetic torques, a phase transition might be possible, and the star might suffer a micro-collapse. If quark deconfinement occurs in NS with a density near the critical one, its structure is re-arranged and part of the energy of the star is used to excite mechanical modes, which will be damped by heat dissipation or gravitational wave emission. The authors determine the rate of micro-collapses using a realistic population synthesis code and find the possible rate of associated gravitational wave detection.
F. Ma [Gen.Relativ. Gravitation 34, No. 8, 1319–1324 (2002; Zbl 1021.83005)] predicted a rate of \(10^{-5}\) formations of stars with quark core after supernovae per year and galaxy. By extrapolation of this result from the Milky Way scales to greater distances, the present authors predict a detection rate of one event per 800 years for the Virgo detector, and of one event per 100 years for the planned advanced Ligo detector. The authors do not expect large changes of these rates if they take the only few existing stars with phase transitions additionally into the account.