Energetics of accretion disk around black holes in Einstein–Gauss–Bonnet gravity

Abstract We investigate the spacetime geometry and astrophysical properties of a static, spherically symmetric black hole in the context of Einstein–Gauss–Bonnet gravity, characterized by a Gauss–Bonnet coupling constant $$\kappa $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>κ</mml:mi> </mml:math> and a non-electromagnetic geometric charge Q . The black hole solution reduces to the Reissner–Nordstrom or Schwarzschild spacetime in the appropriate limits. We analyze the influence of the parameters $$\kappa $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>κ</mml:mi> </mml:math> and Q on the event horizon properties, the innermost stable circular orbit, and the spacetime metric behavior. In the framework of the Novikov–Thorne thin disk model, we compute the flux, temperature, and spectrum of the accretion disk surrounding the black hole. Our results show that the parameters $$\kappa $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>κ</mml:mi> </mml:math> and Q significantly affect the disk’s thermal properties and radiation efficiency. Additionally, we demonstrate that the combined effect of these parameters can mimic the role of spin in Kerr black holes, allowing for degeneracy between rotation and geometric corrections. These findings offer potential observational signatures of modified gravity effects in high-energy astrophysical environments.

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