Dynamical stability of quasitoroidal differentially rotating neutron stars

Espino, Pedro; Paschalidis, Vasileios; Baumgarte, Thomas W.; Shapiro, Stuart L.

doi:10.1103/physrevd.100.043014

Cited by 20 publications

(10 citation statements)

References 92 publications

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“…The largest dephasing between the BHBH and NSNS curves is ≤ 3.5 rads within [0.6, 1.0] KHz. If we extrapolate our results to infinite resolution (see [46,[49][50][51] and our Supplemental Material) we conclude that a BHBH binary will have maximum ∼ 5 rad difference with respect to an NSNS of compaction C = 0.336 in the aforementioned bandwidth. This result is in accordance with other studies [46,52] where typical NSNS binaries are employed and phase differences 20 rad were recorded depending on the EoS, and the NSNS binary properties.…”

Section: As Expected the Nsns Binary Merges Earlier Than Thementioning

confidence: 83%

Great Impostors: Extremely Compact, Merging Binary Neutron Stars in the Mass Gap Posing as Binary Black Holes

et al. 2020

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Can one distinguish a binary black hole undergoing a merger from a binary neutron star if the individual compact companions have masses that fall inside the so-called mass gap of 3 − 5 M ? For neutron stars, achieving such masses typically requires extreme compactness and in this work we present initial data and evolutions of binary neutron stars initially in quasiequilibrium circular orbits having a compactness C = 0.336. These are the most compact, nonvacuum, quasiequilibrium binary objects that have been constructed and evolved to date, including boson stars. The compactness achieved is only slightly smaller than the maximum possible imposed by causality, Cmax = 0.355, which requires the sound speed to be less than the speed of light. By comparing the emitted gravitational waveforms from the late inspiral to merger and post-merger phases between such a binary neutron star vs. a binary black hole of the same total mass we identify concrete measurements that serve to distinguish them. With that level of compactness, the binary neutron stars exhibit no tidal disruption up until merger, whereupon a prompt collapse is initiated even before a common core forms. Within the accuracy of our simulations the black hole remnants from both binaries exhibit ringdown radiation that is not distinguishable from a perturbed Kerr spacetime. However, their inspiral leads to phase differences of the order of ∼ 5 rads over an ∼ 81 km separation (1.7 orbits) while typical neutron stars exhibit phase differences of ≥ 20 rads. Although a difference of ∼ 5 rads can be measured by current gravitational wave laser interferometers (e.g. aLIGO/Virgo), uncertainties in the individual masses and spins will likely prevent distinguishing such compact, massive neutron stars from black holes.

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Section: As Expected the Nsns Binary Merges Earlier Than Thementioning

confidence: 83%

Great Impostors: Extremely Compact, Merging Binary Neutron Stars in the Mass Gap Posing as Binary Black Holes

et al. 2020

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“…Examples of such configurations are reported in Figure 9, where we show meridional energy density contours for a spheroidal and a quasi-toroidal solution. In this paper, we focus primarily on spheroidal models because quasi-toroidal configurations are likely to be unstable [78].…”

Section: Differential Rotationmentioning

confidence: 99%

Maximum mass and universal relations of rotating relativistic hybrid hadron-quark stars

et al. 2019

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We construct equilibrium models of uniformly and differentially rotating hybrid hadron-quark stars using equations of state (EOSs) with a first-order phase transition that gives rise to a third family of compact objects. We find that the ratio of the maximum possible mass of uniformly rotating configurationsthe supramassive limit -to the Tolman-Oppenheimer-Volkoff (TOV) limit mass is not EOS-independent, and is between 1.15 and 1.31, in contrast with the value of 1.20 previously found for hadronic EOSs. Therefore, some of the constraints placed on the EOS from the observation of the gravitational wave event GW170817 do not apply to hadron-quark EOSs. However, the supramassive limit mass for the family of EOSs we treat is consistent with limits set by GW170817, strengthening the possibility of interpreting GW170817 with a hybrid hadron-quark EOSs. We also find that along constant angular momentum sequences of uniformly rotating stars, the third family maximum and minimum mass models satisfy approximate EOS-independent relations, and the supramassive limit of the third family is approximately 16.5 % larger than the third family TOV limit. For differentially rotating spheroidal stars, we find that a lower-limit on the maximum supportable rest mass is 123 % more than the TOV limit rest mass. Finally, we verify that the recently discovered universal relations relating angular momentum, rest mass and gravitational mass for turning-point models hold for hybrid hadron-quark EOSs when uniform rotation is considered, but have a clear dependence on the degree of differential rotation. PACS. 04.40.Dg Relativistic stars: structure, and stability arXiv:1905.00028v1 [astro-ph.HE] 30 Apr 2019 4 Note that this result is in tension with what was found in [85] where different equations of state were adopted. M ↓ M TOV ↓ = 1 + 0.33 J J ↓,Kep 2 − 0.10 J J ↓,Kep 4 . (19)The spread in this equation is at most 2 %. 10 Moreover, we find that the bottom turning points can be described with the same Equations (18), but with a spread of 3 %. The universality becomes tighter if we consider top and bottom turning points separately. For the bottom turning points, the best-fitting functions are M ↓ M TOV ↓ = 1 + 0.35 J M TOV ↓ 2 2 − 0.12 J M TOV ↓ 2 4 , (20a) M 0,↓ M TOV 0,↓ = 1 + 0.58 J M TOV 0,↓ 2 2 − 0.35 J M TOV 0,↓ 2 4

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“…We find that all models witĥ A −1 = 0.4, 0.6, 0.8 are toroidal (i.e., the maximum density is not at the center), and the larger the differential rotation, the more toroidal shapes we were able to compute. Note that according to recent studies [34], extreme toroidal configurations are dynamically unstable. In the T /W panels, we draw with a horizontal dashed-dot line the T /W = 0.25 benchmark, which in many cases provides a crude criterion for the onset of dynamical instability to nonaxisymmetric (bar) modes [35,36].…”

Section: Resultsmentioning

confidence: 76%

Locating ergostar models in parameter space

Tsokaros

Ruiz

Shapiro³

2020

Phys. Rev. D

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Recently, we have shown that dynamically stable ergostar solutions (equilibrium neutron stars that contain an ergoregion) with a compressible and causal equation of state exist [A. Tsokaros, M. Ruiz, L. Sun, S. L. Shapiro, and K. Uryū, Phys. Rev. Lett. 123, 231103 (2019)]. These stars are hypermassive, differentially rotating, and highly compact. In this work, we make a systematic study of equilibrium models in order to locate the position of ergostars in parameter space. We adopt four equations of state that differ in the matching density of a maximally stiff core. By constructing a large number of models both with uniform and differential rotation of different degrees, we identify the parameters for which ergostars appear. We find that the most favorable conditions for the appearance of dynamically stable ergostars are a significant finite density close to the surface of the star (i.e., similar to self-bound quark stars) and a small degree of differential rotation.

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Dynamical stability of quasitoroidal differentially rotating neutron stars

Cited by 20 publications

References 92 publications

Great Impostors: Extremely Compact, Merging Binary Neutron Stars in the Mass Gap Posing as Binary Black Holes

Great Impostors: Extremely Compact, Merging Binary Neutron Stars in the Mass Gap Posing as Binary Black Holes

Maximum mass and universal relations of rotating relativistic hybrid hadron-quark stars

Locating ergostar models in parameter space

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