Physical properties and the maximum compactness bound of a class of compact stars in $f(Q)$ gravity
IUCAA Centre for Astronomy Research and Development ICARD), Department of Physics, Cooch Behar Panchanan Barma University（印度天体物理与宇宙学研究中心（IUCAA）天文研究与开发中心（ICARD），古奇比哈尔潘查南·巴尔马大学物理系）
Motivation: Motivated by the growing interest in understanding the role of non-metricity in describing dense stellar systems, in this paper, we study compact stellar configurations within the framework of linear $f(Q)$ gravity.
Methodology: By adopting a linear modification of the form $f(Q) = αQ+β$, we analyze the internal structure and physical properties of an anisotropic relativistic star within the framework of $f(Q)$ gravity. We employ the Karmarkar's condition together with the Vaidya-Tikekar metric ansatz to obtain a closed-form interior solution of the star. The interior solution is then matched to the Schwarzschild exterior solution across the boundary of the star. By varying the model parameters, we analyze physical features of the resultant stellar configuration.
Results: We note distinctive features in the density, pressure, anisotropy and total mass of the star under a such modification. By enforcing the condition that the central pressure remains finite, we obtain the maximum compactness bound which is shown to depend solely on the Vaidya-Tikekar curvature parameter $K$. We recover the Buchdahl bound for the curvature parameter $K=0$, which corresponds to the solution for an isotropic and homogeneous fluid sphere. Utilizing the energy density and radial pressure profiles, we numerically integrate the modified Tolman-Oppenheimer-Volkoff equations and obtain the mass-radius ($M-R$) relationships for different values of the model parameter $α$. We note that for higher values of $α$, the maximum mass and radius decrease, shifting the stable branch towards ultra-compact configurations. An interesting observation in our analysis is that a linearly modified $f(Q)$ gravity model can support comparatively low mass stars. Utilizing the observed mass of some known pulsars, we demonstrate how our model can be used to fine-tune the radius of the star.
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We are investigating universal relations between different normalisations of the moment of inertia and the compactness of neutron and strange stars. Slowly rotating as well as rapidly rotating models are studied in General Relativity, $\mathcal{R}^2$ gravity and scalar--tensor theories of gravity. Moment of inertia -- compactness relations are examined for different normalisations of the moment of inertia. It is shown that for all studied cases the deviations from EOS universality are small for the examined equations of state. It turns out that in some of the cases the examined relations are a…
A foundational theorem due to Buchdahl states that, within General Relativity (GR), the maximum compactness $\mathcal{C}\equiv GM/(Rc^2)$ of a static, spherically symmetric, perfect fluid object of mass $M$ and radius $R$ is $\mathcal{C}=4/9$. As a corollary, there exists a compactness gap between perfect fluid stars and black holes (where $\mathcal{C}=1/2$). Here we generalize Buchdahl's result by introducing the most general equation of state for elastic matter with constant longitudinal wave speeds and apply it to compute the maximum compactness of regular, self-gravitating objects in GR. W…
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Quark Stars in $f(T,\mathcal{T}) $ Gravity: Structure, Stability, and Observational Constraints
School of Science, Walailak University（瓦拉柴大学理学院）；Research Center for Theoretical Simulation and Applied Research in Bioscience and Sensing, Walailak University（瓦拉柴大学生物科学与传感理论模拟及应用研究中心）；University of KwaZulu-Natal（夸祖鲁-纳塔尔大学）；Eastern Mediterranean University（东地中海大学）；National Institute of Technology, Rourkela（鲁尔克拉国家技术学院）；Saveetha School of Engineering, Saveetha Institute of Medical and Technical Sciences（萨维塔理工学院，萨维塔医学与技术研究所）；Al-Ahliyya Amman University（安曼阿赫利大学）
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