General-relativistic constraints on the equation of state of dense matter implied by kilohertz quasi-periodic oscillations in neutron-star X-ray binaries
Abstract
If the observed millisecond variability in the X-ray flux of several neutron-star low-mass X-ray binaries (LMXBs) is interpreted within a general-relativistic framework (Kluzniak, Michelson \& Wagoner 1990) extant at the time of discovery, severe constraints can be placed on the equation of state (e.o.s.) of matter at supranuclear densities. The reported maximum frequency (1.14 +- 0.01 kHz) of quasiperiodic oscillations observed in sources as diverse as Sco X-1 and 4U 1728-34 would imply that the neutron star masses in these LMXBs are M > 1.9 Msolar, and hence many equations of state would be excluded. Among the very few still viable equations of state are the e.o.s. of Phandaripande and Smith (1975), and e.o.s. AV14 + UVII of Wiringa, Fiks \& Fabrocini (1988).
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