On Thu, 23 Oct 2003 07:13:03 GMT, "Richard Dickison"
wrote:

Why are most galaxies and solar systems 'flat'? If there is a cloud of
dust/gas that starts to coalesce around a localized density in the middle of
the dust/gas, it seems it would attract from all 3 dimensions equally. But
galaxies and solar systems attract primarily in a single plane. What
happened to all the debris above/below the plane?

I understand there will probably be an unequal distribution of matter
surrounding the central object and there will consequently be a resultant
angular momentum after a while. But that doesn't seem to explain why there
still isn't debris spiraling in from above/below the primary plane.

In terms of a Solar System, most of the material that comprises the
final Star/Planet system will be hoovered up by the star in the centre
of the system.

As the cloud shrinks, any rotation in the original cloud will quicken
(the skater bringing their arms in trick) and the remaining material
will tend to flatten out into a disk around the main body (the star).
As the star turns on, any residual material will be vapourised or
blown away.

Heavier material is harder to blow away than lighter gases which is
why the planets nearer the Sun are rocky and the planets further away
are gaseous.

--
Pete
Homepage at http://www.pbl33.co.uk
CCD/digicam astronomy