Neutron Star Interiors and the Equation of State of Superdense Matter
Neutron stars contain matter in one of the densest forms found in the Universe. This feature, together with the unprecedented progress in observational astrophysics, makes such stars superb astrophysical laboratories for a broad range of exciting physical
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Neutron Star Interiors and the Equation of State of Superdense Matter Fridolin Weber, Rodrigo Negreiros, and Philip Rosenfield
10.1 Introduction Neutron stars contain matter in one of the densest forms found in the Universe. This feature, together with the unprecedented progress in observational astrophysics, makes such stars superb astrophysical laboratories for a broad range of exciting physical studies. This paper gives an overview of the phases of dense matter predicted to make their appearance in the cores of neutron stars. Particular emphasis is put on the role of strangeness. Net strangeness is carried by hyperons, K-mesons, H-dibaryons, and strange quark matter, and may leave its mark in the masses, radii, moment of inertia, dragging of local inertial frames, cooling behavior, surface composition, and the spin evolution of neutron stars. These observables play a key role for the exploration of the phase diagram of dense nuclear matter at high baryon number density but low temperature, which is not accessible to relativistic heavy ion collision experiments. Neutron stars are dense, neutron-packed remnants of stars that blew apart in supernova explosions. Many neutron stars form radio pulsars, emitting radio waves that appear from the Earth to pulse on and off like a lighthouse beacon as the star rotates at very high speeds. Neutron stars in X-ray binaries accrete material from a companion star and flare to life with a burst of X-rays. The most rapidly rotating, currently known neutron star is pulsar PSR J1748−2446ad, which rotates at a period of 1.39 ms (which corresponds to a rotational frequency of 719 Hz) [1]. It is followed by PSRs B1937+21 [2] and B1957+20 [3] whose rotational periods are 1.58 ms (633 Hz) and 1.61 ms (621 Hz), respectively. Finally, the recent discovery of X-ray burst oscillations from the neutron star X-ray transient XTE J1739−285 [4] could suggest that XTE J1739−285 contains the most rapidly rotating neutron star yet
F. Weber, R. Negreiros, and P. Rosenfield Department of Physics, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182-1233, USA e-mail: [email protected] W. Becker (ed.), Neutron Stars and Pulsars, Astrophysics and Space Science Library 357, c Springer-Verlag Berlin Heidelberg 2009
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discovered. Measurements of radio pulsars and neutron stars in X-ray binaries comprise most of the neutron star observations. Improved data on isolated neutron stars (e.g., RX J1856.5-3754, PSR 0205+6449) are now becoming available, and future investigations at gravitational wave observatories focus on neutron stars as major potential sources of gravitational waves (see [5] for a recent overview). Depending on star mass and rotational frequency, the matter in the core regions of neutron stars may be compressed to densities that are up to an order of magnitude greater than the density of ordinary atomic nuclei. This extreme compression provides a highpressure environment in which numerous subatomic particle processes are likely to compete
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