  Matter falling onto a black hole is trans-relativistic, transonic, and close
to the horizon it is sub-Keplerian. Such a flow shows the existence of multiple
critical point, shocks etc. Employing relativistic equation of state and
realistic composition, it has been shown that the solution strongly depend on
the composition of the fluid. Electron-positron fluid is the least
relativistic, to the extent that multiple critical points, shocks etc do not
form. The most relativistic fluid is the one whose ratio of proton to electron
number density is ~ 0.2. Since the solution strongly depend on composition, the
emitted radiation should strongly depend on the composition too.
