Recent observations of neutron star masses close to the maximum predicted by
nucleonic equations of state begin to challenge our understanding of dense
matter in neutron stars, and constrain the possible presence of quark matter in
their deep interiors.Comment: To be published in the proceedings of Quark Confinement and the
Hadron Spectrum VII, Sept. 2006, Ponta Delgada, Azores. 7 pages, 3 figures,
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