Mass accretion rate ($\dot{M}$)

The mass accretion rate is the mass entering an accretor per unit time. In a steady spherical flow, $\dot{M}=4\pi r^2\rho u$ is independent of radius.

For a background gravitating density ${\rho }_{\mathrm{dm}}={\Psi }_0{r}^{-5/2}$, the potential is $\Phi =-16\pi G{\Psi }_0{r}^{-1/2}$. A steady polytropic inflow has a regular sonic point only for $1<\gamma <9/7$, and its accretion rate scales as $\dot{M}\propto {\rho }_0{G}^4{\Psi }_0^4{c}_0^{-7}$.