Bondi–Hoyle accretion around the non-rotating black hole in 4D Einstein–Gauss–Bonnet gravity

Abstract

In this paper, the numerical investigation of a Bondi–Hoyle accretion around a non-rotating black hole in a novel four dimensional Einstein–Gauss–Bonnet gravity is investigated by solving the general relativistic hydrodynamical equations using the high resolution shock capturing scheme. For this purpose, the accreated matter from the wind-accreating X-ray binaries falls towards the black hole from the far upstream side of the domain, supersonically. We study the effects of Gauss–Bonnet coupling constant $$\alpha $$ α in 4D EGB gravity on the accreated matter and shock cones created in the downstream region in detail. The required time having the shock cone in downstream region is getting smaller for $$\alpha > 0$$ α > 0 while it is increasing for $$\alpha < 0$$ α < 0 . It is found that increases in $$\alpha $$ α leads violent oscillations inside the shock cone and increases the accretion efficiency. The violent oscillations would cause increase in the energy flux, temperature, and spectrum of X-rays. So the quasi-periodic oscillations (QPOs) are naturally produced inside the shock cone when $$-5 \le \alpha \le 0.8$$ - 5 ≤ α ≤ 0.8 . It is also confirmed that EGB black hole solution converges to the Schwarzschild one in general relativity when $$\alpha \rightarrow 0$$ α → 0 . Besides, the negative coupling constants also give reasonable physical solutions and increase of $$\alpha $$ α in negative directions suppresses the possible oscillation observed in the shock cone.

Dynamical Evolution of the Shock Cone around $4D$ Einstein-Gauss Bonnet Rotating Black Hole

“…According to our initial models, maximum saturation time is observed at α ∼ −5 but it gets smaller when α is increasing. The same behavior was also found for the non-rotating black hole in EGB gravity (Donmez, Orhan 2021). On the other hand, it is seen in Table 1 that the saturation time in EGB gravity converges to Kerr solution in general relativity.…”

“…8 that when α → 0, the black hole solution in EGB gravity converges to Kerr in general relativity. It was also confirmed for the Schwarzschild solution (Donmez, Orhan 2021). In particular, as seen in Figs.…”

“…The amplitude of the genuine mode is getting bigger when α approaches to zero in negative directions. It was also confirmed in the oscillation of the shock cone around the non-rotating black hole in EGB gravity Donmez, Orhan (2021). Similarly, the eigenmodes amplitudes are slightly larger for bigger α.…”

“…In order to understand the effects on Gauss-Bonnet coupling constant α and black hole spin parameter a onto the shock cones, we fixed the values of asymptotic velocity V ∞ = 0.3, the sound speed c s,∞ = 0.1, and adiabatic index Γ = 4/3. More detailed information about handling the initial conditions and other details can also be found in Donmez, Orhan (2021).…”

“…This important feature of EGB gravity starts to pay attention to understand the effects of α to different astrophysical problems around the black hole. In Donmez, Orhan (2021) they explored the properties of the shock cone in a strong gravitation region around the non-rotating black hole in EGB gravity. The cone was produced as a consequence of the Bondi-Hoyle accretion and was connected to the black hole horizon on the downstream side of the computation domain.…”