Why is Andromeda drawn towards the Milky way, and not the other way round?

Andromeda and the Milky Way are gravitationally attracted to each other.

In fact, Andromeda is larger than the Milky Way, so the Milky way is being pulled towards Andromeda *faster* than Andromeda is being pulled towards us. Our galaxy is accelerating faster than theirs is, towards a common center of mass (which is closer to Andromeda than to us, because of their larger mass).

The simplicity of the question indicate a rather childish understanding of physics.

The Andromeda Galaxy IS more massive than the Milky Way. More mass equates to more gravity, and thus, based on gravitational attraction, the Andromeda Galaxy SHOULD be pulling US towards IT.

But this simple-minded explanation totally denies ANY kind of External Influence -- like, possibly the force of the Big Bang itself. What if some force was PUSHING the Andromeda galaxy towards us?

But Einstein had an even better answer -- Relativity. In its simplest form, Einstein says that everything is based on the viewpoint of the observer.

SO, From here on earth it appears the Andromeda is moving towards us. But for some being living on a planet in the Andromeda Galaxy, it appears that we are moving towards them!

So, YOu have a choice:

(1) You need to find out what kind of external forces, other than gravity, might be pushing Andromeda towards us. Is this some kind of result of the Big Bang, or is there some other force -- an as-yet-undiscovered galactic explosion, or even dark matter -- that we don't yet know about or understand.

--OR --

(2) It's all relative to the viewpoint of the observer, They are moving towards us just as fast as we are moving towards them

Just a note that although M31 (the Andromeda Galaxy) is larger and has more stars, the Milky Way might actually be the most massive galaxy in the Local Group. Both galaxies will be moving more or less towards their centre of mass that lies between them. This centre of mass is itself moving as the whole Local Group is being gravitationally dragged upon by the distant but very massive Shapley Supercluster.

Actually you could say that Andromeda is standing still and the Milky Way is heading towards Andromeda. It all just depends on the point of view.

Analogy: we all know that when we see a video of a train driving along that the train is moving while the trees are standing still. But to an observer on the train looking out the window, the trees are moving and the train is standing still!

The relative velocity says the two galaxies are drawn together, or approaching each other. I'm sure the people on a planet orbiting a star in the Andromeda galaxy would consider that the Milky Way is approaching them.

This is not a statement about absolute velocities --- I am unaware of a fixed reference for these kinds of discussions.

Andromeda and the Milky Way are both falling toward each other and toward the center of mass of the Local Group of Galaxies. The Local Group, in turn, is falling into the Virgo Cluster.

Here's a movie of how galaxies move, where each galaxy is a little point of light:

http://www.youtube.com/watch?v=2qeT4DkEX-w

Look at the relative motions of the points of light, not the revolving "camera motion" that gives the 3d effect.

I honestly don't know this as a fact, but I'd say that whenever it's written "andromeda is being pulled towards us", they're really incorrectly saying that the Milky Way and Andromeda are being pulled towards each other. It could also be a matter of relativity, where without a frame of reference, we cannot tell if we are moving towards them, or if they are moving towards us. Only that the distance between us is shortening at a measurable rate.

It's coming towards us from our perspective because we live in the Milky Way. If we lived on Andromeda we'd say the Milky Way is coming towards us. If we had a "god's eye view" we'd say the two galaxies are on a collision course.

Because from our point of view the Milky Way isn't moving, but in reality we are moving just as much as any other galaxy, so yes, the andromeda isn't moving to us, but we're moving towards each other.

It is nothing more than observer bias. An observer from the Virgo cluster would see each galaxy orbiting the common center of mass as the maths suggest.

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