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With the possible detection of the fastest spinning nuclear-powered pulsarXTE J1739-285 of frequency 1122 Hz (0.8913 ms), it arouses us to constrain themass and radius of its central compact object and to imply the stellar mattercompositions: neutrons or quarks. Spun-up by the accreting materials to such ahigh rotating speed, the compact star should have either a small radius orshort innermost stable circular orbit. By the empirical relation between theupper kHz quasi-periodic oscillation frequency and star spin frequency, astrong constraint on mass and radius is obtained as 1.51 solar masses and 10.9km, which excludes most equations of states (EOSs) of normal neutrons andstrongly hints the star promisingly to be a strange quark star. Furthermore,the star magnetic field is estimated to be about $4\times10^{7} (G) < B <10^{9} (G) $, which reconciles with those of millisecond radio pulsars,revealing the clues of the evolution linkage of two types of astrophysicalobjects.

Does Sub-millisecond Pulsar XTE J1739-285 Contain a Low Magnetic Neutron Star or Quark Star ?