  We argue that, when compared to AGNs in dynamical terms, microquasars are
found in low density, low pressure environments. Using a simple analytic model,
we discuss radio lobe dynamics and emission. Dynamical considerations for GRS
1915+105 and GRO J1655-40 show that they are located in ISM densities well
below the canonical n_ISM ~ 1 cm^{-3} unless the jets are unusually narrow or
much more powerful than currently believed.

Astrophysics