Superradiance in modified gravity (MOG)

Abstract

We consider the case of rotating black holes in a dark-matter-emulating theory of gravity called MOG. The latter introduces a gravitational vector field with an associated gravitational charge proportional to the black hole mass and a scalar field in place of the gravitational constant. The resulting black hole metrics resemble the Kerr-Newman geometry and enjoy superradiant scattering. MOG, however, presents important new features. By studying the scattering of a scalar field, we show that there is a marked reduction of the critical frequency of mode amplification. This corresponds to saying that the superradiance peak frequency is red shifted. Analyses of the reflected energy flux also show that MOG black holes are fainter with respect to the standard ones. The proposed results pave the way for testing MOG against astronomical observations.

Overspinning Kerr-MOG black holes by test fields and the third law of black hole dynamics

“…We consider the cases of both extremal and near-extremal black holes. Our analysis exploits the fact that superradiance occurs when scalar fields scatter off Kerr-MOG black holes, which was recently derived by Wondrak, Nicolini, and Moffat [44]. We also evaluate the validity of the third law of black hole dynamics which states that a nearly extremal black arXiv:1907.13435v1 [physics.gen-ph] 24 Jul 2019 hole cannot be driven to extremality by any continuous process.…”

“…Wccc is violated. The scattering of test scalar fields by Kerr-MOG black holes has recently been studied by Wondrak, Nicolini, and Moffat [44]. Analogous to the Kerr case, a neutral wave can be separated into variables in the form…”

“…there is no net absorption of the wave by the black hole. The superradiance limit ω sl for Kerr-MOG black holes is also derived in [44] ω sl = mΩ = ma r 2 + + a 2 (10) where Ω is the angular velocity of the black hole and r + is the spatial location of the event horizon.…”

Exact cosmological black hole solutions in scalar tensor vector gravity

“…2 Different aspects of the STVG black hole solutions have been extensively studied in the literature: accretion disks around Schwarzschild and Kerr STVG black holes [22], shadows cast by near-extremal Kerr STVG black holes [23], black hole superradiance in STVG [24], quasinormal modes of Schwarzschild STVG black holes [25], the process of acceleration and collimation of relativistic jets in Kerr STVG black holes [26], dynamics of neutral and charged particles around a Schwarzschild STVG black hole immersed in a weak magnetic field [27], among others. 3 As suggested by Moffat and Rahvar [9] and Moffat and Toth [36], we dismiss the scalar field ω, and we treat it as a constant, ω = 1.…”

Study of energy extraction and epicyclic frequencies in Kerr-MOG (modified gravity) black hole

“…The gravitational lensing properties of Kerr-MOG has been studied in [19] The Kerr-MOG BH merger and the ringdown radiation have been considered in [26]. The superradiance in Kerr-MOG has been examined in [18] very recently.…”