Speed of sound and quark confinement inside neutron stars

Abstract

Several observations of high-mass neutron stars (NSs), as well as the first historic detection of the binary neutron star merger GW170817, have delivered stringent constraints on the equation of state (EoS) of cold and dense matter. Recent studies suggest that, in order to simultaneously accommodate a 2M⊙ NS and the upper limit on the compactness, the pressure has to swiftly increase with density and the corresponding speed of sound likely exceeds the conformal limit. In this work, we employ a unified description of hadron-quark matter, the hybrid quark-meson-nucleon (QMN) model, to investigate the EoS under NS conditions. We show that the dynamical confining mechanism of the model plays an important role in explaining the observed properties of NSs.

Hybrid neutron stars in the mass‐radius diagram

“…what did the neutron star core transition into, a cold dense quark-gluon plasma or an entirely different exotic state (cf. Marczenko (2020) and references therein). The character of the transition (i.e.…”

The slope, the hill, the drop, and the swoosh: Learning about the nuclear matter equation of state from the binary Love relations

“…2 in [9] and [8,17,19,34,35,39,40,[45][46][47][48][49][50][51][52][61][62][63][64][65][66][67][68][69][70][71][72][73]. Reason (ii) could be related to first-order phase transitions [38,44,52,[74][75][76][77][78] or an "unphase transition", as predicted by the quarkionic model [35,40,42,48,79,80] or crossover transitions/Gibbs constructions to/with (stiff) quark matter [36,37,45,51,[81][82][83]…”

Insights on the peak in the speed of sound of ultradense matter

“…In particular, crucial information is expected from ongoing measurements on the radius of the extremely massive pulsar PSR J0740+6620, by NICER [38]. In light of current observational advances [14-16, 24, 39-44], it seems plausible that future constraints on the masses, radii, and deformabilities of neutron stars will provide extremely compelling evidence in favor of models for the EoS where c s goes above the conformal limit [25,26,[45][46][47][48][49]. If not found in the extremely dense interior of neutron stars, it seems unlikely that violations of the conformal limit might be found elsewhere in the universe.…”