  Building upon the pioneering work [Merle, Rapha\"el, Rodnianski, and Szeftel,
Ann. of Math., 196(2):567-778, 2022, Ann. of Math., 196(2):779-889, 2022,
Invent. Math., 227(1):247-413, 2022] we construct exact, smooth self-similar
imploding solutions to the 3D isentropic compressible Euler equations for ideal
gases for all adiabatic exponents $\gamma>1$. For the particular case
$\gamma=\frac75$ (corresponding to a diatomic gas, e.g. oxygen, hydrogen,
nitrogen), akin to the previous result, we show the existence of a sequence of
smooth, self-similar imploding solutions. In addition, we provide simplified
proofs of linear stability and non-linear stability, which allow us to
construct asymptotically self-similar imploding solutions to the compressible
Navier-Stokes equations with density independent viscosity for the case
$\gamma=\frac75$. Moreover, the solutions constructed have density bounded away
from zero and converge to a constant at infinity, representing the first
example of singularity formation in such a setting.
