One of the most renowned classical experiments that verifies the curved nature of space-time geometry is the bending of light. This phenomenon is extensively discussed in most textbooks on general relativity, with a clear and comprehensive explanation provided. In this study, we employ the material medium approach to determine the refractive index associated with the gravitational field of a compact object with a quadrupole moment. Our research presents a method for calculating the gravitational deflection angle for compact objects by utilizing the refractive index and the GBT theorem for an isotropic metric. This method is particularly important because it allows for the calculation of the deflection angle for both light and relativistic particles. The material medium approach enables us to consider the compact object's gravitational field as a medium with a refractive index. By applying this approach, we establish a relationship between the refractive index and the quadrupole moment of the compact object. We then utilize this relationship to calculate the deflection angle of light and relativistic particles. Одним из самых известных классических экспериментов, подтверждающих искривленную природу геометрии пространства – времени, является искривление света. Обычное объяснение отклонения света простое. Когда присутствует массивный объект, световой луч изгибается под углом, который прямо пропорционален замкнутой массе системы в определенной области, обычно называемой прицельным параметром. Существует новый подход, предлагающий уникальный взгляд на отклонение света в присутствии статического сферически-симметричного гравитационного поля. Этот метод подчеркивает значение топологии траектории световых лучей. Для расчета угла отклонения этот метод использует применение теоремы Гаусса-Бонне. В данной работе мы используем подход материальной среды для определения показателя преломления, связанного с гравитационным полем компактного объекта с квадрупольным моментом. В нашем исследовании представлен метод расчета угла гравитационного отклонения для компактных объектов с использованием показателя преломления и теоремы Гаусса-Бонне для изотропной метрики. Этот метод особенно важен, поскольку позволяет вычислить угол отклонения как для легких, так и для релятивистских частиц. Подход материальной среды позволяет рассматривать гравитационное поле компактного объекта как среду с показателем преломления. Применяя этот подход, мы устанавливаем связь между показателем преломления и квадрупольным моментом компактного объекта. Затем мы используем это соотношение для расчета угла отклонения света и релятивистских частиц. Кеңістік-уақыт геометриясының қисық сипатын растайтын ең әйгілі классикалық тәжірибелердің бірі – жарықтың қисықтығы. Жарықтың ауытқуының әдеттегі түсіндірмесі қарапайым. Массивтік нысан болған кезде, жарық сәулесі әдетте әсер ету параметрі деп аталатын белгілі бір аймақтағы жүйенің жабық массасына тура пропорционал бұрышпен иіледі. Статикалық сфералық симметриялы гравитациялық өріс болған кезде жарықтың ауытқуының бірегей перспективасын ұсынатын жаңа көзқарас бар. Бұл әдіс жарық сәулелерінің траекториясының топологиясының маңыздылығын көрсетеді. Бұл әдіс ауытқу бұрышын есептеу үшін Гаусс-Бонне теоремасын қолдануды пайдаланады. Бұл жұмыста төртполюсті моменті бар ықшам нысанның гравитациялық өрісімен байланысты сыну көрсеткішін анықтау үшін материалдық орта тәсілін қолданамыз. Біздің зерттеуіміз сыну көрсеткішін және изотропты метрика үшін Гаусс-Бонне теоремасын пайдалана отырып, жинақы объектілер үшін гравитациялық ауытқу бұрышын есептеу әдісін ұсынады. Бұл әдіс әсіресе маңызды, себебі ол жеңіл және релятивистік бөлшектер үшін ауытқу бұрышын есептеуге мүмкіндік...

In this work, we study shadows from the naked singularity spacetime. The most analytical solutions of black hole shadows only investigated the case that the geodesic equations for photons can separate variables. We review the spherical null naked singularity metric and this spherically symmetric naked singularity spacetime metric is the solution of Einstein equations with an anisotropic fluid source which has no photon sphere. We also review a static, axially-symmetric singular solution of the vacuum Einstein’s equations without an event horizon which is can be used to describe the exterior gravitational field of a mass distribution with quadrupole moment. Moreover, the corresponding spacetime is characterized by the presence of naked singularities. It is theoretically known that not only a black hole can cast shadow, but other compact objects such as naked singularities, gravastar or boson stars can also cast shadows. We present the analytical calculation of shadows for both naked singularities spacetime and compare with the shadow of Schwarzschild static black hole, we show that this can serve as a black hole mimicker. Keywords: compact object, naked singularity, shadow.

This study examines the equilibrium structure and stability of white dwarfs, incorporating both isotropic and anisotropic pressure distributions. The Tolman–Oppenheimer–Volkoff (TOV) equation is numerically solved using the Chandrasekhar equation of state (EoS) to analyze the effects of pressure anisotropy. A general anisotropy function is introduced to close and solve the system of differential equations. The results indicate that anisotropy remains negligible at the center and increases toward the stellar surface. Stability is assessed using the speed of sound criterion, $v_s^2=dp/d\rho$, and the Buchdahl bound, $2M/R<8/9$, confirming that white dwarfs remain within stability limits. We performed a sensitivity analysis to examine how variations in the anisotropy parameter ${\alpha }_0$ and central density affect the mass, radius, and compactness of white dwarfs. Additionally, we calculated the gravitational redshift at the stellar surface and found that it varies with anisotropy, ranging from $z_s\sim 3.15\times {10}^{-3}$ in isotropic cases to $z_s\sim 0.2\times {10}^{-3}$ in highly anisotropic models. These results link anisotropy to potentially observable features. The findings suggest that while anisotropy does not significantly affect the overall equilibrium structure, it may play a role in astrophysical scenarios involving strong magnetic fields, rotational deformations, or accretion processes in binary systems.

High-mass X-ray binaries (HMXBs) are commonly divided into persistent sources, which emit X-rays steadily over long periods, and transient sources, which remain mostly in a quiescent state and exhibit episodic X-ray outbursts. The aim of this work is to statistically compare the X-ray luminosity properties of these two classes, focusing on the maximum luminosity and the luminosity variability range . For this purpose, catalog data for Galactic HMXB pulsars were used, including 18 persistent and 64 transient systems. The distributions of and were analyzed using histograms, box plots, cumulative distribution functions (CDFs), and the non-parametric Mann–Whitney test. It is shown that both classes reach similar values of on the order of – erg/s), with no statistically significant difference between their distributions. However, transient systems exhibit a much wider luminosity variability range, reaching increases of 4–5 orders of magnitude (up to ), whereas persistent sources typically show lower variability. This difference is statistically confirmed, with transients demonstrating significantly higher variability p ≈ 0.05). Thus, the main distinction between persistent and transient HMXBs lies not in their peak X-ray luminosity, but in their accretion regime. In persistent systems, the compact object continuously accretes matter from a relatively stable stellar wind of an OB supergiant, resulting in steady X-ray emission. In contrast, transient systems are characterized by intermittent accretion (for example, episodic mass capture from a Be-star circumstellar disc), which leads to their extreme luminosity variability.