Universal relations of anisotropic dark energy stars and gravitational-wave constraints

Abstract We investigate, for the first time, universal relations for anisotropic dark energy stars. The stars are modeled with the modified Chaplygin equation of state and the Bowers–Liang prescription for anisotropy, and their global properties and f -mode frequencies are computed using the modified relativistic Hartle–Thorne slow rotation and Cowling approximations. We find that relations among moment of inertia, tidal deformability, quadrupole moment and f -mode frequency exhibit universality, with deviations limited to $$\sim 1{-}10\%$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>∼</mml:mo> <mml:mn>1</mml:mn> <mml:mo>-</mml:mo> <mml:mn>10</mml:mn> <mml:mo>%</mml:mo> </mml:mrow> </mml:math> , in close agreement with other compact star models. Using tidal deformability constraints from GW170817 and GW190814, we obtain astrophysical limits on canonical properties of dark energy stars. For positive anisotropy strength, the radius of a $$1.4M_\odot $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>1.4</mml:mn> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⊙</mml:mo> </mml:msub> </mml:mrow> </mml:math> star is constrained to $$R_{1.4}=8.93^{1.88}_{1.40}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>R</mml:mi> <mml:mrow> <mml:mn>1.4</mml:mn> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>8</mml:mn> <mml:mo>.</mml:mo> <mml:msubsup> <mml:mn>93</mml:mn> <mml:mrow> <mml:mn>1.40</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>1.88</mml:mn> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> km (GW170817) and $$10.92^{+0.71}_{-0.54}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>10</mml:mn> <mml:mo>.</mml:mo> <mml:msubsup> <mml:mn>92</mml:mn> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>0.54</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.71</mml:mn> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> km (GW190814), consistent with observational bounds. The corresponding f -mode frequencies are constrained to $$3.257^{+0.450}_{-0.537}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>3</mml:mn> <mml:mo>.</mml:mo> <mml:msubsup> <mml:mn>257</mml:mn> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>0.537</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.450</mml:mn> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> kHz and $$2.692^{+0.137}_{-0.157}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>2</mml:mn> <mml:mo>.</mml:mo> <mml:msubsup> <mml:mn>692</mml:mn> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>0.157</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.137</mml:mn> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> kHz. Further, applying Pearson correlation analysis for the first time to anisotropic compact stars, we obtained the coefficients between various stellar attributes of dark energy stars and we show that the Chaplygin parameter B correlates strongly with the f -mode frequency, with positive anisotropy strengthening while negative anisotropy weakening the correlation strength. These results establish that universal relations extend to anisotropic dark energy stars and can be directly tested with present and future gravitational-wave observations