Constraining the mass and moment of inertia of neutron star from quasi-periodic oscillations in X-ray binaries

Abstract

Neutron stars are the densest objects known in the Universe. Being the final product of stellar evolution, their internal composition and structure is rather poorly constrained by measurements. We put some constraints on the mass and moment of inertia of these neutron stars based on the interpretation of quasi-periodic oscillations observed in low mass X-ray binaries (LMXBs). More specifically, we use observations of high-frequency quasi-periodic observations (HF-QPOs) to look for the average mass and moment of inertia of neutron stars. This is done by applying our parametric resonance model to discriminate between slow and fast rotators. We fit our model to data from ten LMXBs for which HF-QPOs have been seen and the spin of the enclosed accreting neutron star is known. We find an average mass M * ≈ 2.0 − 2.2 M ⊙ . The corresponding average moment of inertia is then I * ≈ 1 − 3 × 10 38 kg m 2 ≈ 0.5 − 1.5 (10 km) 2 M ⊙ .