Understanding the physical structures of the accreted matter very close to a black hole in quasars and active galactic nucleus (AGN) is an important milestone to constrain the activities occurring in their centers. In this paper, we numerically investigate the effects of the asymptotic velocities on the physical structures of the accretion disk around the Kerr and Einstein–Gauss–Bonnet (EGB) rapidly rotating black holes. The Bondi–Hoyle accretion is considered with a falling gas towards the black hole in an upstream region of the computational domain. Shock cones are naturally formed in the downstream part of the flow around both black holes. The structure of the cones and the amount of the accreted matter depend on asymptotic velocity $V_{\infty }$ (Mach number) and the types of the gravities (Kerr or EGB). Increasing the Mach number of the in-flowing matter in the supersonic region reduces the shock opening angle and the accretion rates, because of the gas rapidly falling towards the black hole. The EGB gravity leads to an increase in the shock opening angle of the shock cones while the mass-accretion rates $dM/dt$ decrease in EGB gravity with a Gauss–Bonnet (GB) coupling constant $\alpha$. It is also confirmed that accretion rates and drag forces are significantly altered in the EGB gravity. Our numerical simulation results could be used in identifying the accretion mechanism and physical properties of the accretion disk and black hole in the observed X-rays such as NGC 1313 X-1 and 1313 X-2 and MAXI J1803-298.

中文翻译：

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克尔域和 4-D Einstein-Gauss-Bonnet 引力域中 Bondi-Hoyle 吸积流的渐近速度研究

了解类星体中非常接近黑洞和活动星系核 (AGN) 的吸积物质的物理结构是限制其中心活动的重要里程碑。在本文中，我们数值研究了渐近速度对快速旋转黑洞周围吸积盘物理结构的影响。Bondi-Hoyle 吸积被认为是在计算域的上游区域向黑洞下落的气体。激波锥自然形成在两个黑洞周围流动的下游部分。锥体的结构和吸积物的数量取决于渐近速度${五}_{\infty }$（马赫数）和重力类型（Kerr 或 EGB）。增加超音速区域流入物质的马赫数会降低激波张角和吸积率，因为气体会迅速落向黑洞。EGB 重力导致激波锥的激波张角增加，而质量吸积率$d米/d吨$EGB 重力随 Gauss-Bonnet (GB) 耦合常数减小$\alpha$. 还证实了吸积率和阻力在 EGB 重力中发生了显着变化。我们的数值模拟结果可用于识别 NGC 1313 X-1 和 1313 X-2 和 MAXI J1803-298 等观测 X 射线中吸积盘和黑洞的吸积机制和物理性质。