Strongly interacting matter exhibits deconfined behavior in massive neutron stars

Abstract

Neutron-star cores contain matter at the highest densities in our Universe. This highly compressed matter may undergo a phase transition where nuclear matter melts into deconfined quark matter, liberating its constituent quarks and gluons. Quark matter exhibits an approximate conformal symmetry, predicting a specific form for its equation of state (EoS), but it is currently unknown whether the transition takes place inside at least some physical neutron stars. Here, we quantify this likelihood by combining information from astrophysical observations and theoretical calculations. Using Bayesian inference, we demonstrate that in the cores of maximally massive stars, the EoS is consistent with quark matter. We do this by establishing approximate conformal symmetry restoration with high credence at the highest densities probed and demonstrating that the number of active degrees of freedom is consistent with deconfined matter. The remaining likelihood is observed to correspond to EoSs exhibiting phase-transition-like behavior, treated as arbitrarily rapid crossovers in our framework.

On the Maximum Mass and Oblateness of Rotating Neutron Stars with Generic Equations of State

“…The median values, together with the 95% error bars, are reported in Table 1. Overall, our results compare well with the corresponding slices calculated by Annala et al (2023), as well as with the results of Gorda et al (2023a), obtained with a Gaussian process regression technique (Landry & Essick 2019).…”

“…All quantities are computed at the center of stellar models with j = 0 (top row) and j = j Kep (bottom row). Vertical black lines are approximate upper bounds reported inAnnala et al (2023) for quark matter in pQCD at n b > 40n s .…”

“…So far, the identification and study of quasi-universal relations has often been limited by the relatively small number of available models. At the same time, a growing number of recent works have explored the possibility of building very large sets of EOSs that satisfy all known theoretical and observational constraints and cover the physically allowed space of EOSs (Landry & Essick 2019;Annala et al 2020) and of related quantities, such as the sound speed (Altiparmak et al 2022;Gorda et al 2023a; or the conformal anomaly (Annala et al 2023;Brandes et al 2023;Marczenko et al 2023). These EOSs are built using either generic piecewise polytropes (see, e.g., Read et al 2009;Kurkela et al 2014;Lattimer & Steiner 2014;Tews et al 2018aTews et al , 2018bMost et al 2018;Steiner et al 2018), a parameterization of the sound speed (see, e.g., Annala et al 2020;Altiparmak et al 2022; or nonparametric Gaussian process regression (see, e.g., Landry & Essick 2019;Gorda et al 2023aGorda et al , 2023b.…”

Constraining Palatini gravity with GR-independent equations of state for neutron stars

“…By analyzing the values of ε − 3P in figure 4, we observe that all the considered EoSs exhibit an energy density interval where the trace becomes negative, consistent with the results of [71,86]. This behavior is dependent on the stiffness of each EoS.…”

Asteroseismology of Compact Stars

“…The equation of state (EOS) for dense matter holds a crucial role in many astrophysical phenomena linked to neutron stars (NSs). Given the non-perturbative properties of strong interaction at low energy, the EOS stands as a key question in both astrophysics and nuclear physics [1][2][3]. The EOS can also be used to infer key aspects of microphysics, such as the role of many-body interactions at nuclear densities.…”