Universality and stationarity of the I-Love relation for self-bound stars

Recently, it was shown that quark matter with only u, d quarks (udQM) can be the ground state of matter for baryon number A > Amin with Amin 300. In this paper, we explore ud quark stars (udQSs) that are composed of udQM, in the context of the two-families scenario in which udQSs and hadronic stars (HSs) can co-exist. Distinct signatures are discussed compared to the conventional study regarding strange quark stars (SQSs). We show that the requirements of Amin 300 and the most-massive compact star observed being udQS together put stringent constraints on the allowed parameter space of udQSs. Then we study the related gravitational-wave probe of the tidal deformability in binary star mergers, including the udQS-udQS and udQS-HS cases. The obtained values of the tidal deformability at 1.4 solar mass and the average tidal deformability are all in good compatibility with the experimental constraints of GW170817/AT2017gfo. This study points to a new possible interpretation of the GW170817 binary merger event, where udQS may be at least one component of the binary system detected.

Section: Properties Of Udqssmentioning

confidence: 59%

Probing up-down quark matter via gravitational waves

Zhang

2020

“…One can also try to find different ways of finding approximate solutions to the Einstein equations that will improve the modeling. The model presented here does not apply to stellar solutions whose density does not vanish at the surface, such as quark stars and self-bound stars [43]. It would be interesting to construct analytic interior models appropriate for these kinds of stars.…”

Section: Discussionmentioning

confidence: 99%

Improved analytic modeling of neutron star interiors

Jiang

Yagi

2019

Studies of neutron stars are extremely timely given the recent detection of gravitational waves from a binary neutron star merger GW170817, and an International Space Station payload NICER currently in operation that aims to determine radii of neutron stars to a precision better than 5%. In many cases, neutron star solutions are constructed numerically due to the complexity of the field equations with realistic equations of state. However, in order to relate observables like the neutron star mass and radius to interior quantities like central density and pressure, it would be useful to provide an accurate, analytic modeling of a neutron star interior. One such solution for static and isolated neutron stars is the Tolman VII solution characterized only by two parameters (e.g. mass and radius), though its agreement with numerical solutions is not perfect. We here introduce an improved analytic model based on the Tolman VII solution by introducing an additional parameter to make the analytic density profile agree better with the numerically obtained one. This additional parameter can be fitted in terms of the stellar mass, radius and central density in an equationof-state-insensitive way. In most cases, we find that the new model more accurately describes realistic profiles than the original Tolman VII solution by a factor of 2-5. Our results are first-step calculations towards constructing analytic interior solutions for more realistic neutron stars under rotation or tidal deformation. arXiv:1904.05954v3 [gr-qc]

“…[52]. Quasi-universal I-compactness relations predate the I-Love-Q relations in the literature [11,[53][54][55], but generally exhibit a lesser degree of equation-of-state independence [1,56]. Ref.…”

Section: I-compactness Relationmentioning

confidence: 92%

Inferring neutron star properties from GW170817 with universal relations

Kumar

Landry

2019

Because all neutron stars share a common equation of state, tidal deformability constraints from the compact binary coalescence GW170817 have implications for the properties of neutron stars in other systems. Using equation-of-state insensitive relations between macroscopic observables like moment of inertia (I), tidal deformability (Λ) and stellar compactness, we derive constraints on these properties as a function of neutron-star mass based on the LIGO-Virgo collaboration's canonical deformability measurement, Λ1.4 = 190 +390 −120 . Specific estimates of Λ, I, dimensionless spin χ, and stellar radius R for a few systems targeted by radio or X-ray studies are extracted from the general constraints. We also infer the canonical neutron-star radius as R1.4 = 10.9 +1.9 −1.5 km at 90% confidence. We further demonstrate how a gravitational-wave measurement of Λ1.4 can be combined with independent measurements of neutron-star radii to tighten constraints on the tidal deformability as a proxy for the equation of state. We find that GW170817 and existing observations of six thermonuclear bursters in low-mass X-ray binaries jointly imply Λ1.4 = 196 +92 −63 at the 90% confidence level.1 A different universal relation has been used elsewhere in conjunction with GW170817 to constrain the maximum mass of nonrotating neutron stars [26]. 2 In the remainder of the paper, quoted error bars refer to symmetric 90% confidence intervals about the median unless otherwise specified. 3 Note added: A Bayesian analysis of this kind-but focused on the stellar radius, rather than the tidal deformability-is presented in Ref.[45], which appeared shortly after completion of this paper.