Fast pulsar in SN 1987A: Candidate for strange-quark matter

All known pulsar frequencies and masses can be accounted for by plausible neutron-star models with the exception of the new fast pulsar. To withstand its rotation frequency the central density of the star must be so high that the constituents cannot be individual hadrons. If strange-quark matter (u,d,s quarks) is the absolute ground state, a star of such matter can be stable against mass loss at the frequency of the new pulsar. An essential difference between neutron stars and strange stars is the binding force, gravity for ordinary stars, and confinement and gravity in the case of strange stars