We investigate the properties of low angular momentum, inviscid, advective accretion flows in a generic static and spherically symmetric spacetime that incorporates higher-order corrections up to the fourth order in $1/r$. Employing this metric, we self-consistently solve the relativistic hydrodynamical equations and obtain the family of global transonic accretion solutions (O, A, W, and I types) by means of the spacetime parameters $(\delta ,\eta ,\beta )$ and the flow parameters (specific energy $\mathcal{E}$ and angular momentum $\lambda$). Our analysis reveals that the accretion flow possesses either single or multiple critical points depending on these input parameters. We delineate the regions of the $\delta -\lambda$ and $\lambda -ℰ$ parameter spaces that admits solutions with multiple critical points and demonstrate how these regions evolve with increasing spacetime parameter $\delta$. Furthermore, while connecting the spacetime geometry with observable signatures, we compute the spectral energy distribution (SED) from thermal bremsstrahlung emission and observe that increasing $\delta$ enhances the SED relative to the Schwarzschild case. Finally, we find that global transonic solutions harboring inner critical points (I types) yield more luminous power than those with only outer critical points (O and A types).

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• Accretion disk & black-hole plasma
• Hydrodynamics