arXiv subjects

R. H. Ali

Publications and source records attributed to R. H. Ali.

5 recordsLinked to original sources

arXiv2026

Periodic Timelike Motion and Gravitational Wave Signatures around a Magnetically Charged Black Hole Surrounded by Quintessence

We investigate timelike geodesics and gravitational wave signatures of periodic motion around a static magnetically charged black hole arising from nonlinear electrodynamics and immersed in a quintessence background. We analyze the effective potential for massive particles, determine the marginally bound and innermost stable circular orbits, and classify the resulting bound trajectories using the zoom-whirl taxonomy $(\mathit{z},\mathit{w},\mathit{v})$. We show that the quintessence parameter $c_q$ systematically shifts the orbital radii, conserved quantities, and turning-point structure associated with representative periodic families. We then model the gravitational radiation emitted by periodic extreme-mass-ratio inspirals within the numerical kludge approximation. The resulting waveforms exhibit the characteristic burst-like structure of zoom-whirl motion, while variations in the quintessence coupling parameter modify the phase evolution, burst timing, and harmonic content of the signal. The corresponding Fourier spectra display a discrete comb-like structure, and the characteristic strain is concentrated in the millihertz band relevant for space-based detectors such as LISA. These results indicate that a quintessence background can leave systematic imprints on periodic orbit dynamics and on the associated time and frequency-domain gravitational wave observables.

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arXiv2026

Precessions and parameter constraints from quasiperiodic oscillations in a rotating charged black hole

We investigate quasi-periodic oscillations (QPOs) as a diagnostic tool for probing frame-dragging effects and accretion disk physics in the spacetime of a rotating regular magnetic black hole (BH). Specifically, we analyze the precession of bound orbits and the epicyclic oscillations of test particles under small perturbations in the equatorial plane. We demonstrate how the BH nonminimal coupling parameter (lambda/M^4) and dimensionless magnetic charge (Q/M) significantly influence the three fundamental epicyclic frequencies. By applying the relativistic precession model and employing Markov Chain Monte Carlo simulations (MCMC), we constrain the BH characteristic parameters, including mass, spin, magnetic charge, and nonminimal coupling, using observational QPO data from five X-ray binaries: GRO J1655-40, XTE J1859+226, H1743-322, XTE J1550-564, and GRS 1915+105. Furthermore, we examine the Lense-Thirring, geodetic, and general spin precession frequencies of a test gyroscope attached to a stationary observer around the black hole. Our theoretical results indicate that the regular charged black hole suppresses these precession frequencies compared with the Kerr black hole case.

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arXiv2025

Mapping Quasi-Periodic Oscillations to Lyapunov Exponent across Black Hole Thermodynamic Phase Transitions

We investigate the thermodynamic phase structure of a nonminimally coupled magnetic AdS black hole through the dynamics of timelike particles. The free energy analysis reveals a Van der Waalslike phase transition characterized by small, intermediate, and large black hole phases. We show that both the Lyapunov exponent of unstable circular orbits and the quasi-periodic oscillation (QPO) frequencies associated with stable circular orbits exhibit clear signatures of underlying thermodynamic phase structure, including first order and critical phase transitions. More importantly, we establish a QPO-Lyapunov exponent mapping and demonstrate that the resulting relation inherits the same thermodynamic branch structure. Although the Lyapunov exponent and QPO frequencies originate from unstable and stable circular orbits, respectively, their correspondence emerges from the common black hole spacetime geometry and remains valid even in the absence of phase transitions. Our results reveal an unexplored connection among orbital instability, QPO phenomenology, and black hole thermodynamics, suggesting a potential observational route for probing chaotic orbital dynamics and thermodynamic phases through QPO measurements.

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arXiv2023

Thermal fluctuations, quasi-normal modes and phase transition of the charged AdS black hole with perfect fluid dark matter

In this paper, we study thermodynamics, thermal fluctuations, phase transitions and the charged anti-de Sitter black hole surrounded by perfect fluid dark matter. Large black holes are shown to be stable when subject to thermal fluctuations, and we begin by exploring how these fluctuations affect the uncorrected thermodynamic quantities of entropy, Helmholtz free energy, Gibbs free energy, enthalpy specific heat, and phase transition stability. We also discuss null geodesics and the radius of the photon sphere for the charged AdS BH and use the radius of a photon sphere to calculate the Lyapunov exponent and angular velocity. Exceptionally, we test the effects of various parameters of a black hole graphically by observing the existence of the correction parameter and the coupling parameter, which reveal the behavior of corrected thermodynamic quantities. Lastly, we see how the system is stable (under the effects of the dark matter parameter) by figuring out the specific heat and Hawking temperature, which are both related to entropy.

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arXiv2023

Extended phase space thermodynamics of black hole with non-linear electrodynamic field

This paper deals with the thermodynamical properties of black hole formulated in Einstein theory of relativity and associated with a nonlinear electromagnetic field. The transition of the black hole is analyzed using the parameters mass, electric charge, coupling constant, and cosmological constant. We find-out the thermodynamical aspects of exact black hole solutions to compute the black hole mass, temperature, entropy, Gibbs free energy, specific heat and the critical exponents in the phase space. Further, we study the stability of the black hole solution by specific heat and Gibbs free energy. We look at the first and second phase changes and show a P-V criticality, which is like the Van der Waals phase change. We also examine the equation of the state and the critical exponents.

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