Galactic Motions

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? You can get the radial
velocity from the Doppler shift, but how can they know the angular velocity?
Isn't it more likely that it's just gravitationally bound?

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

"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?

Probably not.

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

Not sure about angular, but we certainly don't know about the transverse
velocity. Chances are we'll miss each other.

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

Most likely it is, since we're both part of the local cluster.

"Topquark" wrote in
:

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? You can get the radial velocity from the Doppler shift, but how
can they know the angular velocity? Isn't it more likely that it's
just gravitationally bound?


That is most likely the case but both galaxies cover a fair bit of real
estate so their centres could be more than 200,000 ly apart at closest
approach and you would still get interaction.

LK

"T" == Topquark writes:

T A program on the Science Channel [...] mentioned that the galaxy in
T Andromeda M31 is moving toward us and will therefore collide with
T our galaxy some time in the future--They showed simulations.

See URL:http://www.cita.utoronto.ca/~dubinski/tflops/.

T Is this true? You can get the radial velocity from the Doppler
T shift, but how can they know the angular velocity? Isn't it more
T likely that it's just gravitationally bound?

Well, if we're going to collide, we're still gravitationally bound.
Even the angular velocity would not make that much difference,
though. It may make the process longer, but it will not change the
final outcome. Galaxies seem to have a lot more matter than we can
detect from their radiation. This includes the Milky Way. These
extended dark halos will interact and cause the two galaxies to spiral
together.

--
Lt. Lazio, HTML police | e-mail:
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html