Galaxies

Local Group

15.13 - Understand why galaxies are grouped in larger clusters and superclusters

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15.4 - Know that the group of galaxies gravitationally linked to the Milky Way is called the Local Group

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15.5 - Know the composition and scale of the Local Group, including its principal components:
a) Andromeda Galaxy (M31)
b) Large and Small Magellanic Clouds (LMC and SMC)
c) Triangulum Galaxy (M33)

Galaxies are not always solitary bodies. They are frequently grouped together and sometimes interact or even collide. Usually groups comprise of up to 50 galaxies and these groups are connected to superclusters of groups throughout the universe.

The Milky way lies in the middle of a group of fifty galaxies that we give the imaginative name of the 'local group'. The Milky Way and Andromeda Galaxy are the largest bodies and it is thought a common centre of gravity lies between the two. The local group is part of a larger group again called the Virgo Supercluster.

The Milky Way is actually converging with a smaller galaxy, the Sagittarius Dwarf galaxy. In several million years' time, the larger spiral Andromeda galaxy (M31) will converge with the Milky Way and form an even larger galaxy.

We also have companion galaxies orbiting very close to the Milky Way in the form of Magellanic Clouds, after which was named after the explorer Magellan when he ventured into the Southern Hemisphere. The nearest galaxy, the irregular dwarf Large Magellanic Cloud orbits just 170,000 light years away from us. The similar Small Magellanic Cloud is slightly further, while the Andromeda Galaxy, the largest galaxy in the Local Group is 2 million light years away. Other notable galaxies include the spiral Triangulum Galaxy (M33) which is a satellite galaxy of Andromeda.

The Andromeda and Triangulum galaxies are named after the constellation in which they appear.