Massive compact stars beyond two solar masses: quark stars admixed with dark matter in regularized 4D Einstein–Gauss–Bonnet gravity

Abstract We investigate massive compact stars composed of quark matter admixed with bosonic dark matter in regularized four-dimensional Einstein–Gauss–Bonnet gravity. The stellar interior is modeled as a two-fluid system, in which quark matter follows the MIT bag model and dark matter is described by self-interacting bosonic particles in the Thomas–Fermi regime. Numerical integration of the modified Tolman–Oppenheimer–Volkoff equations reveals that positive Gauss–Bonnet coupling significantly enhances the maximum gravitational mass, with configurations reaching up to $$2.5~M_{\odot }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>2.5</mml:mn> <mml:mspace/> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⊙</mml:mo> </mml:msub> </mml:mrow> </mml:math> , thereby enabling compact stars to exceed two solar masses. The resulting mass–radius relations are consistent with observational constraints from GW170817, PSR J0348+0432, PSR J0952-0607, and HESS J1731-347. Comprehensive stability analysis shows that the equilibrium sequences satisfy the Harrison–Zeldovich–Novikov static stability criterion up to the maximum-mass turning point, while representative stable-branch configurations exhibit adiabatic indices exceeding $$\gamma =4/3$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>γ</mml:mi> <mml:mo>=</mml:mo> <mml:mn>4</mml:mn> <mml:mo>/</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:math> and maintain subluminal sound speeds throughout the stellar interior. Our results demonstrate that the combined effects of quark matter, dark matter, and higher-curvature corrections provide a robust framework for describing ultra-massive compact stars in the multi-messenger era.