Gravitational Instability
Key Concepts:
Wrinkles represent "hills" and "valleys"
Matter falls into and accumulates in valleys
Dense objects such as galaxies form
in the valleys
If we have small wrinkles or hills and valleys early on in the
universe, matter will tend to fall into the valleys, eventually
producing dense regions that become the sites of galaxies.
In the discussion that follows, I will often represent these
wrinkles by a sort of "top view" where the color coding refers
to the density of matter (dark regions have more matter, light
regions less).
Needless to say, this is a bit of an idealization for illustative purposes.
Cosmologists actually run computer simulations to track how matter
collects into valleys. For example, here is a simulation running
forward in time which shows how particles collect and enhance small
initially small wrinkles
(simulation and movie courtesy of Andrey Kravtsov)
