Re: Where is the Milky Way going?

Gary - this is a great question. I learned quite a bit in trying to answer it! I agree with you that `Voyage to the great Attractor' is a very good book, and now I'm trying to find a copy of `Coming of Age in the Milky Way'..

One way people answer the question of where the Milky Way is going is to look at the cosmic microwave background. This is the radiation left over from the big bang, and there is a particular reference frame in which it will look isotropic (the same in all directions). By checking whether or not the radiation looks isotropic to us we can tell if we are moving with respect to the reference frame.

It turns out that we are moving, towards the direction of the constellation Leo (RA: 11.2h, dec: -7deg), at about 380 km/s. But this includes the motion of the Sun around the Milky Way and the motion of the Milky Way around the center of the Local Group of galaxies. (These add up to about 300 km/s in the direction of the constellation Cygnus.) After correcting for these we find that the Local Group of galaxies is moving at about 600 km/s (relative to the cosmic microwave background) in the direction of the Hydra-Centaurus supercluster. This is the reason for Dressler and collaborators' idea that there must be something pulling us in that direction (the `Great Attractor'), but there are a lot of tricky details involved in how you figure this out, and not everyone agrees with their idea.

I'm not sure if the Milky Way is moving in a different direction from the galaxies around us or not - this isn't something I've heard of before. But I don't think I'd go so far as to say that's evidence of divine intervention. I can't think of a particular reason why going in a different direction would be better, especially since it would take a very long time to get anywhere.

Pauline