Isothermal Bondi equation (source code)

= Isothermal Bondi equation
{c}

For inward speed $u>0$, steady spherical mass conservation and radial momentum balance give
$$
\left(u-\frac{c_s^2}{u}\right)\frac{du}{dr}
=\frac{2c_s^2}{r}-\frac{GM}{r^2}.
$$