Impact of extended gravity theories on accretion dynamics and observables in black hole

Abstract

We examine a thin accretion disk surrounding a static, spherically symmetric black hole within the framework of Einstein–Gauss–Bonnet massive gravity theory. Our focus is on the motion of particles in circular orbits around the black hole in this spacetime. Specifically, we study the geodesic motion of particles confined to the equatorial plane, which contributes to the formation of the thin accretion disk, to explore their innermost stable circular orbits and energy flux distribution. To provide a comprehensive analysis of our study, we present density plots of the effective potential, specific energy, angular momentum, angular velocity, and radiation flux. The contour plots reveal that the massive gravity and Gauss–Bonnet parameters significantly influence the gravitational pull and energy dissipation within the accretion disk. These effects have important implications for the observational properties of black holes in extended gravity theories, impacting the disk’s brightness and thermal spectrum. Utilizing the well-established Novikov–Thorne model for accretion, we investigate the impact of Gauss–Bonnet and massive gravity parameters on the direct and secondary images of the black hole’s accretion disk at various observation angles. Notably, we observe significant deviations from standard black hole solutions, such as Schwarzschild or Reissner–Nordstrm.