Impact of massive neutron star radii on the nature of phase transitions in dense matter

Abstract

The last few years have seen tremendous progress in the observation of the global properties of neutron stars (NSs), e.g. masses, radii and tidal deformabilities. Such properties provide information about possible phase transitions in the inner cores of NSs, provided the connection between observed masses and radii and the equation of state (EoS) is well understood. We focus the present study on first-order phase transitions, which often softens the EoS and consequently reduces the maximum mass as well as the radii of NSs. Here, we challenge this conventional expectation by constructing explicit examples of EoSs undergoing a first-order phase transition, but which are much stiffer that their purely hadronic counterparts. We also provide comparisons with the recently proposed quarkyonic EoS which suggests a strong repulsion in the core of NSs, and we show that their stiffness can be realistically masqueraded by first-order phase transitions to exotic matter.

Impact of the PSR J0740+6620 radius constraint on the properties of high-density matter

“…in [55,56]. This effectively rules only out the most extreme case of phase transitions that led to a 2 km decrease in radii [107] but still remains consistent with milder or smooth phase transitions [100,109]. In the case of multiple stable branches, we find that the maximum c 2 s is higher than the single-branch case, though this does not seem to affect the ∆R marginalized posterior.…”

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

“…Fig. 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]…”

Impact of NICER's Radius Measurement of PSR J0740+6620 on Nuclear Symmetry Energy at Suprasaturation Densities

“…Combined with NICER's earlier simultaneous mass and radius measurement of PSR J0030+0451 (Miller et al 2019;Riley et al 2019), the first radius measurement of the most massive NS has the strong potential to reveal interesting new physics about the Equation of State (EOS) of super-dense neutron-rich nuclear matter. Besides earlier predictions about what uniquely new physics can be learned from the radii of massive NSs compared to canonical ones, see, e.g., Xie & Li (2020); Han & Prakash (2020); Drischler et al (2021); Somasundaram & Margueron (2021), several new analyses aiming at extracting new information about the EOS of super-dense matter from NS observations including the latest NICER observations have already been carried out (Biswas 2021;Li et al 2021;Raaijmakers et al 2021;Pang et al 2021). In this Letter, we show that the 68% lower mass-radius boundary of R 2.01 ≥ 12.2 km (Miller et al 2021) provides a much tighter lower boundary than previously known for nuclear symmetry energy in the density range of (1.0 ∼ 3.0)ρ 0 .…”