The effect of rotation on the properties of neutron stars

Magdalena Szkudlarek, Dorota Gondek-Rosińska, Marcus Ansorg and Loic Villain

Neutron stars (NS) are the densest, fastest rotating, and the most stable objects in the Universe, the density in their interior is even higher than the nuclear density. The real form of matter in such high densities is still unknown. There are many hypotheses about realistic equation of state (EoS): from very simple with neutrons, protons, electrons and muons, through more complex with hyperon condensates or super uidity to the exotic ones with strange quark matter or kaon or pion condensation in the stellar core. Independently of EoS, rotation has an important impact on the properties of NSs. A newly born, hot NS rotates differentially (the closer to the stellar centre the higher spin velocity is). Cold NSs rotate uniformly, since any fluctuations are suppressed by high viscosity of the matter. The rotation frequency is limited by the mass-shedding frequency (the Keplerian limit) when the centrifugal force on the surface is equal to the gravitational force. The theoretical limits on uniform rotation are 0.4 ms to 1.2 ms for different EoS of NSs (Cook et al., 1994) and 0.36 ms to 0.6 ms for strange quark stars (SQS) (Gourgoulhon et al., 1999; Gondek-Rosińska et al., 2000). The fastest observed NS is a pulsar PSR J1748-2446ad, rotating with 1.4 ms (Hessels et al., 2006). The difference between observed frequency and theoretical one can be explained by gravitational wave emission - rotating star could lose its angular momentum by breaking axial symmetry. Rotation may have important impact on the properties of NS, e.g., it can increase their masses, radii, decrease central density and significantly change their shapes. In the article we summarize the results on the effect of the rotation (uniform and differential) on the properties of NSs (including SQSs). We present the first relativistic, numerical results of differentially rotating SQSs.

Proceedings of the Polish Astronomical Society, vol. 1, 132-135 (2014)

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