Is there a way of inverting this function to obtain $r(\rho)$?
rho[r_, b0_, q_] :=
r (1 + (Sqrt[\[Pi]]Gamma[1Sqrt[π]Gamma[1/(q - 1)])/((1 - q) Gamma[1/2 ((q + 1)/(q - 1))]) b0 /r + (1 + q)/(2 q) (b0/r)^(1 - q))
Note that $q<0$ and $b0$ is some positive constant.