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Title: Implications of NICER for Neutron Star Matter: The QHC21 Equation of State
Abstract

The recent NICER measurement of the radius of the neutron star PSR J0740+6620, and the inferred small variation of radii from 1.4 to 2.1M, reveal key features of the equation of state of neutron star matter. The pressure rises rapidly in the regime of baryon densityn∼ 2–4 times nuclear saturation density,n0—the region where we expect hadronic matter to be undergoing transformation into quark matter—and the pressure in the nuclear regime is greater than predicted by microscopic many-body variational calculations of nuclear matter. To incorporate these insights into the microscopic physics from the nuclear to the quark matter regimes, we construct an equation of state, QHC21, within the framework of quark–hadron crossover. We include nuclear matter results primarily based on the state-of-the-art chiral effective field theory, but also note results of using nuclear matter variational calculations based on empirical nuclear forces. We employ explicit nuclear degrees of freedom only up ton∼ 1.5n0, in order to explore the possibility of further physical degrees of freedom than nucleonic here. The resulting QHC21, which has a peak in sound velocity in ∼2–4n0, is stiffer than the earlier QHC19 below 2n0, predicting larger radii in substantial agreement with the NICER data.

 
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NSF-PAR ID:
10374403
Author(s) / Creator(s):
; ;
Publisher / Repository:
DOI PREFIX: 10.3847
Date Published:
Journal Name:
The Astrophysical Journal
Volume:
934
Issue:
1
ISSN:
0004-637X
Format(s):
Medium: X Size: Article No. 46
Size(s):
["Article No. 46"]
Sponsoring Org:
National Science Foundation
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