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The Puzzles of RX J1856.5-3754: Neutron Star or Quark Star?

J. E. Truemper·V. Burwitz·F. Haberl·V. E. Zavlin
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Abstract

We discuss recent Chandra and XMM-Newton observations of the bright isolated neutron star RX J1856.5-3754 and suggest that the absence of any line features is due to effects of a high magnetic field strength (~10^13 G). Using different models for the temperature distribution across the neutron star surface assuming blackbody emission to fit the optical and X-ray spectrum and we derive a conservative lower limit of the "apparent" neutron star radius of 16.5 km x (d/117 pc). This corresponds to the radius for the "true" (de-redshifted) radius of 14 km for a 1.4 Msun neutron star, indicating a stiff equation of state at high densities. A comparison of the result with mass-radius diagrams shows that quark stars and neutron stars with quark matter cores can be ruled out with high confidence.

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J. E. Truemper, V. Burwitz, F. Haberl, V. E. Zavlin. 2003-12-23. The Puzzles of RX J1856.5-3754: Neutron Star or Quark Star?. https://doi.org/10.1016/j.nuclphysbps.2004.04.094

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