TY - JOUR
T1 - Constraints on the equation of state of neutron star matter from observations of kilohertz QPOs
AU - Miller, M. Coleman
AU - Lamb, Frederick K.
AU - Psaltis, Dimitrios
N1 - Funding Information:
This work was supported in part by NASA grant NAG 5-2868 at the University of Chicago and by NSF grants AST 93-15133 and AST 96-18524 and NASA grant NAG 5-2925 at the University of Illinois.
PY - 1999/1
Y1 - 1999/1
N2 - The frequencies of the highest-frequency kilohertz QPOs recently discovered in some sixteen neutron stars in low-mass X-ray binary systems are most likely the orbital frequencies of gas in Keplerian orbit around these neutron stars. If so, these QPOs provide tight upper bounds on the masses and radii of these neutron stars and important new constraints on the equation of state of neutron star matter. If the frequency of a kilohertz QPO can be established as the orbital frequency of gas at the innermost stable circular orbit, this would confirm one of the key predictions of general relativity in the strong-gravity regime. If the spin frequency of the neutron star can also be determined, the frequency of the QPO would fix the mass of the neutron star for each assumed equation of state. Here we show how to derive mass and radius bounds, using the kilohertz QPOs, for nonrotating and slowly rotating stars, and discuss how these bounds are affected by rapid stellar rotation and radial radiation forces. We also describe observational results that would be strong evidence for the presence of an innermost stable circular orbit. No such strong evidence is present in current data, but future prospects are excellent.
AB - The frequencies of the highest-frequency kilohertz QPOs recently discovered in some sixteen neutron stars in low-mass X-ray binary systems are most likely the orbital frequencies of gas in Keplerian orbit around these neutron stars. If so, these QPOs provide tight upper bounds on the masses and radii of these neutron stars and important new constraints on the equation of state of neutron star matter. If the frequency of a kilohertz QPO can be established as the orbital frequency of gas at the innermost stable circular orbit, this would confirm one of the key predictions of general relativity in the strong-gravity regime. If the spin frequency of the neutron star can also be determined, the frequency of the QPO would fix the mass of the neutron star for each assumed equation of state. Here we show how to derive mass and radius bounds, using the kilohertz QPOs, for nonrotating and slowly rotating stars, and discuss how these bounds are affected by rapid stellar rotation and radial radiation forces. We also describe observational results that would be strong evidence for the presence of an innermost stable circular orbit. No such strong evidence is present in current data, but future prospects are excellent.
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U2 - 10.1016/s0920-5632(98)00194-7
DO - 10.1016/s0920-5632(98)00194-7
M3 - Article
AN - SCOPUS:0032622858
VL - 69
SP - 123
EP - 128
JO - Nuclear and Particle Physics Proceedings
JF - Nuclear and Particle Physics Proceedings
SN - 2405-6014
IS - 1-3
ER -