{
  "id": "2106.05313",
  "version": "v1",
  "published": "2021-06-09T18:08:05.000Z",
  "updated": "2021-06-09T18:08:05.000Z",
  "title": "Impact of the PSR J0740+6620 radius constraint on the properties of high-density matter",
  "authors": [
    "Isaac Legred",
    "Katerina Chatziioannou",
    "Reed Essick",
    "Sophia Han",
    "Philippe Landry"
  ],
  "comment": "18 pages, 11 figures",
  "categories": [
    "astro-ph.HE",
    "gr-qc",
    "nucl-th"
  ],
  "abstract": "X-ray pulse profile modeling of PSR J0740+6620, the most massive known pulsar, by the NICER and XMM-Newton observatories recently led to a measurement of its radius. We investigate this measurement's implications for the neutron star equation of state, employing a nonparametric EoS model based on Gaussian processes and combining information from other X-ray, radio and gravitational-wave observations of neutron stars. Our analysis mildly disfavors equations of state that support a disconnected hybrid star branch in the mass-radius relation, a proxy for strong phase transitions, with a Bayes factor of 6.4. For EoSs with multiple stable branches, the transition mass from the hadronic to the hybrid branch is constrained to lie outside ($1, 2$) $M_{\\odot}$. We also find that the conformal sound-speed bound is violated inside neutron star cores, implying that core matter is strongly interacting. The squared sound speed reaches a maximum of $0.79^{+0.21}_{-0.26}c^2$ at $3.51^{+2.30}_{-1.76}$ times nuclear saturation density at 90% credibility. Since all but the gravitational-wave observations prefer a relatively stiff EoS, PSR J0740+6620's central density is only $3.0^{+1.6}_{-1.6}$ times nuclear saturation, limiting the density range probed by observations of cold, nonrotating neutron stars in $\\beta$-equilibrium.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2021-06-09T18:08:05.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "high-density matter",
      "radius constraint",
      "times nuclear saturation density",
      "properties",
      "violated inside neutron star cores"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 18,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}