Radiation field around black holes in f (R, T ) gravity: circular orbits and QPOs
Аннотация
Abstract We study circular geodesics and quasi-periodic oscillations (QPOs) around a static black hole in f (R, T ) gravity surrounded by a Kiselev radiation field with equation of state parameter w = 1/3. Starting from the exact analytic solution, we introduce an effective mass function and show how the radiation parameter K and the f (R, T ) coupling γ deform the black hole geometry, reducing the effective gravitational mass near the black hole while recovering the standard behavior at large radii. For electrically neutral test particles, we derive the effective potential, the specific energy and angular momentum of circular orbits, and the characteristics of the innermost stable circular orbit (ISCO), the marginally bound orbit (MBO), and the marginally circular orbit (MCO), highlighting their dependence on the radiation field. We then compute the Keplerian (orbital) and radial/vertical epicyclic frequencies along ISCOs and analyse how the radiation field and f (R, T ) couplings modify these dynamical frequencies. Finally, we confront the model with twin-peak QPO observations from the microquasars XTE J1550-564 and GRO J1655-40, the intermediate-mass black hole M82 X-1, and Sgr A* by applying the relativistic precession (RP) and warped-disk (WD) QPO models. Using χ 2 minimization, we perform Monte Carlo Markov Chain (MCMC) simulations to constrain the parameters (M, α, K, γ, rQPO). Our fits show that the RP model provides consistent descriptions for GRO J1655-40, M82 X-1, and Sgr A*, while the WD model is mainly favored for XTE J1550-564, and that the inferred values of K and γ are largely degenerate between the two QPO scenarios.