The neutron star radius and the dense-matter equation of state

Mar 27, 2014, 4:35 PM


Sebastien Guillot (M)


A physical understanding of the behaviour of cold ultra-dense matter - at and above nuclear density - can only be achieved by the study of neutron stars, and the thermal emission from quiescent low-mass X-ray binaries inside globular clusters have proven very useful for that purpose. The recent 1.97±0.04 Msun measurement for the radio pulsar PSR 1614-2230 suggests that strange quark matter and hyperons/kaons condensate equations of states (EoS) are disfavoured, in favour of hadronic "normal matter" EoSs. Over much of the neutron star mass-radius parameter space, "normal matter" EoSs produce lines of quasi-constant radii (within the measurement uncertainties, of about 10%). We present a simultaneous spectral analysis of several globular cluster quiescent low-mass X-ray binaries where we require the radius to be the same among all neutron stars analyzed. The Markov-Chain Monte-Carlo method and the Bayesian approach developed in this analysis permits including uncertainties in the distance, in the hydrogen column density, and possible contributions to the spectra due to un-modelled spectrally hard components. Our results suggest a neutron star radius much smaller than previously reported, with a value Rns = 9.1±1.4 km, at 90% confidence, using conservative assumptions, which suggests that neutron start matter is best described by the softest "normal matter" equations of state.

Primary author


Dr Mathiey Servillat (CEA Saclay) Dr Natalie Webb (IRAP/CNRS) Prof. Robert Rutledge (McGill University)

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