  This paper is devoted to a rigorous derivation of the isentropic
Euler-alignment system with singular communication weights $\phi_\alpha(x) =
|x|^{-\alpha}$ for some $\alpha > 0$. We consider a kinetic BGK-alignment model
consisting of a kinetic BGK-type equation with a singular Cucker-Smale
alignment force. By taking into account a small relaxation parameter, which
corresponds to the asymptotic regime of a strong effect from BGK operator, we
quantitatively derive the isentropic Euler-alignment system with pressure
$p(\rho) = \rho^\gamma$, $\gamma = 1 + \frac2d$ from that kinetic equation.
