Dear Topquark:

"Topquark" wrote in message
...
A program on the Science Channel last night talked about black holes in
the
center of galaxies. It also mentioned that the galaxy in Andromeda M31
is
moving toward us and will therefore collide with our galaxy some time in
the
future--They showed simulations. Is this true?

Yes.

You can get the radial
velocity from the Doppler shift, but how can they know the angular
velocity?

The average radial velocity of all visible objects/systems in Andromeda has
it coming towards us. Velocity around its common center is unimportant.
Its center, based on the average( left & right), and leading edge is coming
this way.

Isn't it more likely that it's just gravitationally bound?

That too. We have possibly done this particular step before, and will
likely do it again.

David A. Smith