Abstract
At supranuclear densities, explored in the core of neutron stars, a strong phase transition from hadronic matter to more exotic forms of matter might be present. To test this hypothesis, binary neutron-star mergers offer a unique possibility to probe matter at densities that we can not create in any existing terrestrial experiment. In this work, we show that, if present, strong phase transitions can have a measurable imprint on the binary neutron-star coalescence and the emitted gravitational-wave signal. We construct a new parameterization of the supranuclear equation of state that allows us to test for the existence of a strong phase transition and extract its characteristic properties purely from the gravitational-wave signal of the inspiraling neutron stars. We test our approach using a Bayesian inference study simulating 600 signals with three different equations of state and find that for current gravitational-wave detector networks already twelve events might be sufficient to verify the presence of a strong phase transition. Finally, we use our methodology to analyze GW170817 and GW190425, but do not find any indication that a strong phase transition is present at densities probed during the inspiral.
Highlights
Neutron stars (NSs) are remnants of core-collapse supernovae and contain matter at the highest densities that we can observe in the Universe, up to several times nuclear saturation density, nsat = 0.16 fm−3, which corresponds to a mass density of 2.7×1014 g cm−3
The major differences between previous studies and our work are that we simultaneously (i) analyze equation of state (EOS) with different phase-transition signatures, i.e., one EOS with a twin-star solution which is commonly searched for, and two EOSs with phase transitions leading to single-branch solutions; (ii) analyze both simulated data and actual events with state-of-the-art Bayesian gravitational waves (GWs) data analysis techniques, which allows for hypothesis testing and parameter estimation at once; and (iii) explicitly demonstrate that our method is able to measure the microscopic characteristics of strong phase transitions by comparing injected with recovered parameters
We have presented a reliable way of searching for phase transitions in supranuclear matter using the inspiral waveform of binary NS mergers, which is successful if the resulting mass-radius relation has only one or multiple stable branches
Summary
We focus on three different EOS that experience a phase transition in the typical mass range explored in BNS systems and which show three different behaviors in the mass-radius relation For this purpose, we introduce a method, based on a new parametrization for EOSs at supranuclear densities, of testing GW data from the inspiral phase of a BNS merger for the appearance of a strong phase transition. The major differences between previous studies and our work are that we simultaneously (i) analyze EOSs with different phase-transition signatures, i.e., one EOS with a twin-star solution which is commonly searched for, and two EOSs with phase transitions leading to single-branch solutions; (ii) analyze both simulated data and actual events with state-of-the-art Bayesian GW data analysis techniques, which allows for hypothesis testing and parameter estimation at once; and (iii) explicitly demonstrate that our method is able to measure the microscopic characteristics of strong phase transitions by comparing injected with recovered parameters.
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