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

Legred, Isaac and Chatziioannou, Katerina and Essick, Reed and Han, Sophia and Landry, Philippe (2021) Impact of the PSR J0740+6620 radius constraint on the properties of high-density matter. Physical Review D, 104 (6). Art. No. 063003. ISSN 2470-0010. doi:10.1103/physrevd.104.063003.

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X-ray pulse profile modeling of PSR J0740+6620, the most massive known pulsar, with data from 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 (EoS), 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 EoSs that support a disconnected hybrid star branch in the mass-radius relation, a proxy for strong phase transitions, with a Bayes factor of 6.9. For such EoSs, the transition mass from the hadronic to the hybrid branch is constrained to lie outside (1,2) M_⊙. We also find that the conformal sound-speed bound is violated inside neutron star cores, which implies that the core matter is strongly interacting. The squared sound speed reaches a maximum of 0.75^(+0.25)_(−0.24) c² at 3.60^(+2.25)_(−1.89) 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 3.57^(+1.3)_(−1.3) times nuclear saturation, limiting the density range probed by observations of cold, nonrotating neutron stars in β-equilibrium.

Item Type:Article
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URLURL TypeDescription Paper ItemData
Legred, Isaac0000-0002-9523-9617
Chatziioannou, Katerina0000-0002-5833-413X
Essick, Reed0000-0001-8196-9267
Han, Sophia0000-0002-9176-4617
Landry, Philippe0000-0002-8457-1964
Additional Information:© 2021 American Physical Society. (Received 10 June 2021; revised 27 July 2021; accepted 28 July 2021; published 2 September 2021) Research at Perimeter Institute is supported in part by the Government of Canada through the Department of Innovation, Science and Economic Development Canada and by the Province of Ontario through the Ministry of Colleges and Universities. S. H. is supported by the National Science Foundation, Grant No. PHY-1630782, and the Heising-Simons Foundation, Grant No. 2017-228. P. L. is supported by National Science Foundation Grant No. PHY-1836734 and by a gift from the Dan Black Family Foundation to the Nicholas & Lee Begovich Center for Gravitational-Wave Physics & Astronomy. This research has made use of data, software and/or web tools obtained from the Gravitational Wave Open Science Center (, a service of LIGO Laboratory, the LIGO Scientific Collaboration and the Virgo Collaboration. Virgo is funded by the French Centre National de Recherche Scientifique (CNRS), the Italian Istituto Nazionale della Fisica Nucleare (INFN) and the Dutch Nikhef, with contributions by Polish and Hungarian institutes. This material is based upon work supported by NSF’s LIGO Laboratory which is a major facility fully funded by the National Science Foundation. The authors are grateful for computational resources provided by the LIGO Laboratory and supported by National Science Foundation Grants No. PHY-0757058 and No. PHY-0823459.
Funding AgencyGrant Number
Department of Innovation, Science and Economic Development (Canada)UNSPECIFIED
Ontario Ministry of Colleges and UniversitiesUNSPECIFIED
Heising-Simons Foundation2017-228
Dan Black Family FoundationUNSPECIFIED
Centre National de la Recherche Scientifique (CNRS)UNSPECIFIED
Istituto Nazionale di Fisica Nucleare (INFN)UNSPECIFIED
Issue or Number:6
Record Number:CaltechAUTHORS:20210927-213255867
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:111059
Deposited By: George Porter
Deposited On:27 Sep 2021 22:37
Last Modified:28 Sep 2021 20:40

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