Possible signatures for strange stars in stellar X-ray binaries

Kilohertz quasi-periodic brightness oscillations (kHz QPOs) observed in cer tain X-ray burst sources may represent Keplerian frequencies in the inner r egions of the accretion disk in such systems. If this assumption is strictl y adhered to, we show here that if the central accretor in stellar X-ray bu rst sources is a strange star (made up of u, d and s quarks in beta equilib rium, referred to as strange matter) then the calculated QPO frequencies ar e reconcilable with the observed QPO frequencies (corresponding to the high est frequency of 1.22 kHz, observed so far from the source 4U 1636-53) only for particular values of the QCD-related parameters which describe the equ ation of state of strange matter. We demonstrate that QPO frequencies in th e very high range (1.9-3.1) kHz can be understood in terms of a (non-magnet ized) strange star X-ray binary (SSXB) rather than a neutron star X-ray bin ary (NSXB). Future discovery of such high frequency QPOs from X-ray burst s ources will constitute a new astrophysical diagnostic for identifying solar mass range stable strange stars in our galaxy.