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| Format: | Preprint |
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2025
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| Online Access: | https://arxiv.org/abs/2504.08662 |
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| _version_ | 1866915245205749760 |
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| author | Zhou, Tianzhe Huang, Chun |
| author_facet | Zhou, Tianzhe Huang, Chun |
| contents | The twin star configuration, where two neutron stars share the same mass but exhibit different radii, arises from a strong first-order phase transition within the stellar interior. In widely used equation of state (EoS) meta-models, such as the Polytrope (PP) and Speed-of-Sound (CS) models, this first-order phase transition behavior can be naturally mimicked by tuning some model parameters. Here, we systematically explore the under-explored parameter space within one of a widely adopted CS model that leads to twin stars via a strong first-order phase transition. Within this twin-star subspace, we perform a comprehensive Bayesian analysis that integrates mass--radius (MR) constraints from X-ray observations of rotation-powered millisecond pulsars. The resultant twin star branch, situated within the 1--1.2 $M_{\odot}$ mass range and approximately 7 km in radius, surprisingly coincides with the MR ranges proposed for the recent anomaly in the Accreting Millisecond X-ray Pulsars XTE J1814--338 (J1814), suggesting a hybrid twin star configuration. Moreover, incorporating the J1814 observation as an additional constraint yields an extreme phase transition pressure $P_{\text{trans}} = 108.9_{-4.85}^{+6.46}$ MeV/fm$^3$, a transition density of $\varepsilon_{\text{trans}}/\varepsilon_0 = 4.847_{-0.134}^{+0.271}$(where $\varepsilon_0$ is the nuclear saturation energy density) and an energy density jump $Δ\varepsilon = 558.7_{-278.7}^{+303.6}$ MeV/fm$^3$, corresponding to $Δ\varepsilon/\varepsilon_0 = 3.716_{-1.854}^{+2.020}$. Notably, to satisfy all astrophysical constraints, the speed of sound inside of the hybrid twin star core is driven toward the speed of light ($c_s^2/c^2 > 0.9$), indicating the potential presence of strongly interacting, exotic matter in this core region. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2504_08662 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Hidden Twin Star Solutions from an Agnostic Speed-of-Sound Model: Confronting XTE J1814--338's Extreme Compactness Zhou, Tianzhe Huang, Chun High Energy Astrophysical Phenomena General Relativity and Quantum Cosmology Nuclear Theory The twin star configuration, where two neutron stars share the same mass but exhibit different radii, arises from a strong first-order phase transition within the stellar interior. In widely used equation of state (EoS) meta-models, such as the Polytrope (PP) and Speed-of-Sound (CS) models, this first-order phase transition behavior can be naturally mimicked by tuning some model parameters. Here, we systematically explore the under-explored parameter space within one of a widely adopted CS model that leads to twin stars via a strong first-order phase transition. Within this twin-star subspace, we perform a comprehensive Bayesian analysis that integrates mass--radius (MR) constraints from X-ray observations of rotation-powered millisecond pulsars. The resultant twin star branch, situated within the 1--1.2 $M_{\odot}$ mass range and approximately 7 km in radius, surprisingly coincides with the MR ranges proposed for the recent anomaly in the Accreting Millisecond X-ray Pulsars XTE J1814--338 (J1814), suggesting a hybrid twin star configuration. Moreover, incorporating the J1814 observation as an additional constraint yields an extreme phase transition pressure $P_{\text{trans}} = 108.9_{-4.85}^{+6.46}$ MeV/fm$^3$, a transition density of $\varepsilon_{\text{trans}}/\varepsilon_0 = 4.847_{-0.134}^{+0.271}$(where $\varepsilon_0$ is the nuclear saturation energy density) and an energy density jump $Δ\varepsilon = 558.7_{-278.7}^{+303.6}$ MeV/fm$^3$, corresponding to $Δ\varepsilon/\varepsilon_0 = 3.716_{-1.854}^{+2.020}$. Notably, to satisfy all astrophysical constraints, the speed of sound inside of the hybrid twin star core is driven toward the speed of light ($c_s^2/c^2 > 0.9$), indicating the potential presence of strongly interacting, exotic matter in this core region. |
| title | Hidden Twin Star Solutions from an Agnostic Speed-of-Sound Model: Confronting XTE J1814--338's Extreme Compactness |
| topic | High Energy Astrophysical Phenomena General Relativity and Quantum Cosmology Nuclear Theory |
| url | https://arxiv.org/abs/2504.08662 |