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Rescaling strange-cluster stars and its implications on gravitational-wave echoes

Chen Zhang, Yong Gao, Cheng-Jun Xia, and Renxin Xu
Phys. Rev. D 108, 063002 – Published 1 September 2023
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  • INTRODUCTION
  • DIMENSIONLESS RESCALING OF STRANGEON
  • RESCALING STRANGEON STARS
  • GW ECHOES FROM STRANGEON STARS
  • DIMENSIONAL PARAMETER SPACE
  • SUMMARY
  • ACKNOWLEDGMENTS
    • References

    Abstract

    Solid states of strange-cluster matter called strangeon matter can form strangeon stars that are highly compact. We show that strangeon matter and strangeon stars can be recast into dimensionless forms by a simple reparametrization and rescaling, through which we manage to maximally reduce the number of degrees of freedom. With this dimensionless scheme, we find that strangeon stars are generally compact enough to feature a photon sphere that is essential to foster gravitational-wave (GW) echoes. Rescaling the dimension back, we illustrate its implications on the expanded dimensional parameter space, and calculate the characteristic GW echo frequencies associated with strangeon stars, showing that the minimum echo frequency is ∼8  kHz for empirical parameter space that satisfies the GW170817 constraint, and can reduce to O(100) Hertz at the extended limit.

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    • Received 17 May 2023
    • Accepted 7 August 2023

    DOI:https://doi.org/10.1103/PhysRevD.108.063002

    © 2023 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Exotic phases of matterGravitational wave sourcesGravitational wavesNuclear matter in neutron starsQuark matter
    1. Physical Systems
    Neutron stars & pulsars
    Gravitation, Cosmology & Astrophysics

    Authors & Affiliations

    Chen Zhang1,*, Yong Gao2,3,†, Cheng-Jun Xia4,‡, and Renxin Xu2,3,§

    • 1The HKUST Jockey Club Institute for Advanced Study, The Hong Kong University of Science and Technology, Hong Kong, People’s Republic of China
    • 2Department of Astronomy, School of Physics, Peking University, Beijing 100871, China
    • 3Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, China
    • 4Center for Gravitation and Cosmology, College of Physical Science and Technology, Yangzhou University, Yangzhou 225009, China

    • *iasczhang@ust.hk
    • †gaoyong.physics@pku.edu.cn
    • ‡cjxia@yzu.edu.cn
    • §r.x.xu@pku.edu.cn

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    Issue

    Vol. 108, Iss. 6 — 15 September 2023

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    Images

    • Figure 1
      Figure 1

      M¯−R¯ of strangeon stars for various ε¯, sampling 0.0001–0.13 in equal Δε¯ spacing from the lighter black line to the darker black lines, respectively. Solid dots denote the maximum mass configurations.

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    • Figure 2
      Figure 2

      Maximum compactness Cmax=MTOV/RTOV (left axis, black) and M¯TOV (right axis, red) of strangeon stars as a function of ε¯.

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    • Figure 3
      Figure 3

      Λ−M¯ of strangeon stars for various ε¯. The line-color convention follows that of Fig. 1.

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    • Figure 4
      Figure 4

      Radial profiles of effective potentials for axial gravitational perturbations of the l=s=2 mode in strangeon-star background at MTOV points for various ε¯. The color convention of black lines follows that of Fig. 1. The red line denotes the ε¯=0.175≈ε¯maxtheo limit.

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    • Figure 5
      Figure 5

      Rescaled echo frequencies f¯echo as functions of center pressure p¯c of strangeon stars for various ε¯. The color convention of black lines follows that of Fig. 1. The red line denotes the ε¯=0.175≈ε¯maxtheo limit.

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    • Figure 6
      Figure 6

      Physical parameter space for (top) Nq=18 and (bottom) Nq=9. Black lines denote fecho/kHz, with red lines denoting the maximum masses MTOV/M⊙, green lines for the tidal deformabilities Λ at 1.4M⊙ and blue dotted lines for the maximal compactness MTOV/RTOV.

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