In this series we are exploring the weird and wonderful world of astronomy jargon! Get your friends together to talk about today’s topic: the Local Group!
The Local Group is the name for the collection of galaxies near the Milky Way. In total it’s about 10 million light-years across and contains over 80 galaxies, although most of those galaxies are very small dwarf galaxies.
The Milky Way itself dominates one side of the Local Group and is by far the largest object in its nearest vicinity. Many dwarf galaxies orbit the Milky Way, including the two Magellanic Clouds that are visible to the naked eye. On the other side of the Group sits Andromeda, another massive spiral galaxy about 2.5 million light-years away from, along with all of its satellite galaxies. Both the Milky Way and Andromeda have masses around 10^12 times that of the Sun, and each one contains several hundred billion stars.
The third largest member of the Group is Triangulum, which has a mass of about 50 billion solar masses. Triangulum sits about 750,000 light-years away from Andromeda.
All the members of the Local Group are gravitationally bound, meaning that their mutual gravitational attraction will keep them together. The Milky Way and Andromeda are moving towards each other, and will eventually collide in about 5 billion years.
The Local Group is a part of the Virgo Supercluster, and is moving towards the Virgo Cluster, which is about 60 million light-years away. Zooming out even further, the Virgo Supercluster is a small branch of a much larger supercluster called Laniakea.