Jeans Mass and the
Growth of Perturbations
Growth of Perturbations
The universe is NOT
static, however. Were interested in
the problem in an
expanding universe. But the
characteristic timescale
for expansion is related to the Hubble time (chap. 13):
This time is
comparable to the time of exponential growth when gravity dominates, and modifies the above
result. Note, not the Hubble constant here H varies with time.
Combes et al.
introduces the scale factor R(t), also a(t) in other textbooks. So
for an expanding universe, use the coordinates r = R(t) x, and v = dR(t)/dt x + R(t) u so the expansion can be included. So
now rewrite the hydrodynamic equations.
