Phantom black holes in f(R,T) gravity: From circular orbits to QPO tests

Cosmological and astrophysical observations, combined with theoretical studies, may help us understand the nature of dark matter. In this work, we focus on the dynamics of particles around a black hole surrounded by exotic matter known as a phantom field, which exhibits anti-gravitating behavior within the framework of f(R,T) gravity. First, we investigate the spacetime properties of the black hole, particularly the black hole horizon, the effective gravitational mass of the spacetime, and scalar invariants such as the Ricci scalar, the square of the Ricci tensor, and the Kretschmann scalar. We also examine the circular motion of test particles, including innermost stable circular orbits (ISCOs), minimum circular orbits (MCOs), and marginally bound orbits (MBOs) taking into account interaction between the scalar field and particles as a fifth force. In the next step, we study particle oscillations near the black hole in the presence of the phantom field. We investigate the frequencies of Keplerian orbits and radial oscillations, and apply these findings to the twin-peaked quasiperiodic oscillations (QPOs) within the relativistic precession model. Finally, to obtain constraint values, we analyze the phantom field, equation of state and fifth interaction parameters, as well as the mass of phantom black holes in f(R,T) gravity, using QPOs observed in microquasars XTE J1550-564, GRO J1655-40, and GRS 1915 +105, as well as in galaxies M82-X1 and around the Milky Way, employing Markov Chain Monte Carlo (MCMC) analyses. Our results indicate that the obtained values of the phantom field and black hole parameters can explain the observed QPO frequencies in these objects, suggesting that this modified gravity theory may remain consistent with the observations.