Parameter estimation for strong phase transitions in supranuclear matter using gravitational-wave astronomy

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 cannot 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 parametrization 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 12 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.

Extreme Matter meets Extreme Gravity: Ultra-heavy neutron stars with crossovers and first-order phase transitions

“…10. Examples of all three classes have appeared previously in the literature from both phenomenological EoS models [14,15,45,[145][146][147][148][149][150], as well as more realistic nuclear physics models [16, 46, 49, 52-60, 63, 64, 67, 109, 151-153]. For example, a disconnected mass twin sequence arises from a nuclear-physics-based EoS driven by strangeness, as shown in Fig.…”

“…Result 5: First-order phase transitions in heavy neutron stars M ≥ 2 M . We are able to generate a number of EoSs that lead to disconnected twins that reach a maximum mass larger than M ≥ 2 M , in contrast to [45], due to non-trivial structure in c 2 s . The large maximum mass can occur in either the first or second stable branch.…”

“…Twin stars were first proposed in [42] for the general case of first-order phase transitions, and in [43] for the specific case of deconfinement to quark matter. Recently, twins have been thoroughly studied in the case of a constant speed of sound for quark matter [13,14,44], polytropes [45] or using two different EoSs, one of which is easily adjustable [46]. The second stable-branch family appears when (i) the central stellar density reaches the threshold for a strong first-order phase transition, creating an unstable region in the mass-radius diagram, and when (ii) there is a large enough portion of the star made up of matter that reaches densities beyond the transition threshold and described by a stiff enough EoS.…”

Future Physics Perspectives on the Equation of State from Heavy Ion Collisions to Neutron Stars

“…First-order phase transitions are signaled by a region where the speed of sound is equal to zero. If a strong first order phase transition between hadronic matter and quark matter was experienced within a neutron star merger, this would have consequences for the ringdown and the remnants [11,[82][83][84][85][86][87][88]. In addition, if a strong first-order line occurs at zero temperature, it is possible that mass twins could be produced wherein two neutron stars have the same mass but very different radii [89][90][91][92][93].…”

Differentiating between sharp and smoother phase transitions in neutron stars

“…In general, a state transition between distinct phases of matter results in a softening of the pressure-density relation in the equation of state (EOS), which in turn results in more compact NSs (in terms of stellar parameters, this is quantified by larger values of the compactness parameter GM/Rc 2 , with M denoting the gravitational mass, and R the stellar radius), and a lower maximum mass M max than in the case of stars without state transitions, due to transitional deficit in pressure increase related to the softening. While a direct access to the interiors of NS is impossible, one can draw conclusions from astrophysical measurements of the stellar mass M and radius R with the use of * jpereira@camk.edu.pl electromagnetic observables (see, e.g., [9][10][11][12][13]), as well as the tidal deformabilities Λ i of the components of a binary system during its last orbits before the merger by means of gravitational wave (GW) signals ( [14][15][16][17][18][19][20], see also [21] for a review), due to their dependence on the EOS; hence, one can expect potentially measurable imprints of densematter state transitions on these NS observables. For recent reviews on the dense-matter state transitions in NSs, see e.g., [22,23].…”