With the possible detection of the fastest spinning nuclear-powered pulsar XTE J1739-285 of frequency 1122 Hz ( 0.8913 ms ) , it arouses us to constrain the mass and radius of its central compact object and to imply the stellar matter compositions : neutrons or quarks .
Spun-up by the accreting materials to such a high rotating speed , the compact star should have either a small radius or short innermost stable circular orbit .
By the empirical relation between the upper kHz quasi-periodic oscillation frequency and star spin frequency , a strong constraint on mass and radius is obtained as 1.51 solar masses and 10.9 km , which excludes most equations of states ( EOSs ) of normal neutrons and strongly hints the star promisingly to be a strange quark star .
Furthermore , the star magnetic field is estimated to be about 4 \times 10 ^ { 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 astrophysical objects .