Is the Local Group expanding along with the entire Universe? (Intermediate)

The Local Group of Galaxies (Milky Way, Andromeda, etc) moves towards the Local Supercluster. At the same time, are our neighbour Galaxies getting away from Milky Way? Is the Local Group expanding as a whole thing at the same time that the further universe is expanding ?

Our nearest galactic neighbors, namely the Local Group, consists mainly of our galaxy, the Andromeda galaxy, the Large and Small Magellanic Clouds as well as about 30 small galaxies within ~1-2 Mpc from us. The two largest galaxies, the Milky Way and the Andromeda, are moving towards each other at about 119 km/s instead of expanding along with the rest of the universe because the gravitational attraction between the two is stronger. In fact, the entire Local Group is collapsing under the gravitational attraction, and in about 3 billion years, the Milky Way and Andromeda will collide! Ahhhh!

On a larger scale, the Local Group is moving towards the Local Supercluster at about 600 km/s, but it doesn't head straight for the center of the Local Supercluster as expected. In fact, we see "peculiar motions", or motions in directions different than those we would expect based on the expansion of the universe, in many structures in the local universe, from nearby galaxies to larger galaxy clusters. By building maps of these peculiar motions in the relatively local universe (you can see an example of this work here), astronomers can get a better idea about how mass is distributed within the local universe, as it is the gravitational attraction between these objects that prevents them from moving apart as the universe expands. 

This is a very fun page about The Structure of the Universe that lets you see different structures, from the nearest neighboring stars to the entire universe.

This page was last updated on January 28, 2019

About the Author

Lisa Wei

Lisa graduated from Cornell in May 2004 with a Bachelors in Astronomy. While here she studied frost streaks on Mars and the substructures in the Virgo Cluster. She is now a graduate student in Astronomy at the University of Maryland.

Here is a list of some questions answered by Lisa (2003-2004).