On perturbation induced minimal geometric decoupling in spacetime and its impact on mass-gap stability: Insights from the binary mergers GW190814, GW200210, and millisecond pulsars PSR J1614-2230 and PSR J0952-0607

Singh K.N. Maurya S.K. Errehymy A. Umbetova Z. Myrzakulov K. Rayimbaev J.
February 2026 Elsevier B.V.

Journal of High Energy Astrophysics
2026 #50

This study investigates the internal composition and stability of mass-gap compact stars (CSTARs) formed from neutron star mergers or evolved massive pulsars, using the minimal geometric deformation (MGD) framework. Starting from a Buchdahl–Vaidya–Tikekar inspired metric ansatz, we derive exact, physically consistent unperturbed solutions describing static, spherically symmetric stars with energy densities monotonically decreasing from central values on the order of 10¹⁵g/cm³ to the surface at radius R . To model realistic astrophysical effects such as gravitational waves or accretion, we introduce a perturbation function g(r)=sin⁡(ωr²) characterized by amplitude α and frequency ω . Rather than assuming a fixed EOS, we adopt a well-defined ansatz for the metric component g_rr (Eq. (21) ), inducing pressure-density relations confirmed through radial profiles of pressure and density. We incorporate observational constraints from pulsars PSR J1614-2230 (1.97_−0.04^+0.0M_⊙), PSR J0952-0607 (approximately 2.35M_⊙), and gravitational wave events GW190814 and GW200210, which suggest masses above 2M_⊙. Radius estimates such as 13.70_−1.5^+2.6km for PSR J0740+6620 provide additional bounds. As α increases from 0 to 0.005, the EOS shifts sharply from linear to nonlinear. In contrast, increasing ω up to 0.06km⁻² with fixed α=0.001 causes only minor EOS deviations. The mass-radius (M−R) relation is similarly affected: without perturbations (α=0, ω=0), the curve is smooth, reaching a maximum mass M_max≈3.5M_⊙ with radius R≈12km. For α=0.001, raising ω to 0.015km⁻² produces radius fluctuations of δR≈0.17km near M≈2.7M_⊙ and R≈13.3km. Increasing α beyond 0.001 induces stronger oscillations in mass and radius, with mass exceeding 3.5M_⊙ and radius surpassing 12km. These perturbations soften the EOS, reducing M_max and thus hindering collapse into black holes. The M−R curves respect the Buchdahl limit (2MR<89) and intersect observational bands for massive objects, supporting physical viability. The amplitude α plays a dominant role in anisotropy growth, sound speed behavior (both radial and tangential remain subluminal), and adiabatic index Γ, which stays above the critical threshold for stability. Frequency ω has a secondary but non-negligible effect, causing small radius oscillations but preserving overall dynamic stability against radial perturbations. In summary, small perturbations—particularly amplitude α —strongly affect the structure, EOS, and stability of mass-gap neutron stars (NSTARs), aligning well with observations.

EOS , Mass-gap CSTARs , MGD , NSTAR mergers

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Department of Physics and Astrophysics, University of Delhi, New Delhi, 110007, India
Department of Mathematical and Physical Sciences, College of Arts and Sciences, University of Nizwa, Nizwa, 616, Oman
Astrophysics Research Centre, School of Mathematics, Statistics and Computer Science, University of KwaZulu-Natal, Private Bag X54001, Durban, 4000, South Africa
Center for Theoretical Physics, Khazar University, 41 Mehseti Str., Baku, AZ1096, Azerbaijan
Department of General and Theoretical Physics, L.N. Gumilyov Eurasian National University, Astana, 010008, Kazakhstan
Institute of Fundamental and Applied Research, National Research University TIIAME, Kori Niyoziy 39, Tashkent, 100000, Uzbekistan
National University Uzbekistan, Tashkent, 100174, Uzbekistan
University of Tashkent for Applied Science, Str. Gavhar 1, Tashkent, 100149, Uzbekistan
Tashkent State Technical University, Tashkent, 100095, Uzbekistan
Urgench State University, Kh. Alimjan Str. 14, Urgench, 221100, Uzbekistan

Department of Physics and Astrophysics
Department of Mathematical and Physical Sciences
Astrophysics Research Centre
Center for Theoretical Physics
Department of General and Theoretical Physics
Institute of Fundamental and Applied Research
National University Uzbekistan
University of Tashkent for Applied Science
Tashkent State Technical University
Urgench State University

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