GALACTIC EVOLUTION

How different sizes can affect how these gigantic structures form

SMALL GALAXIES 1 A lonely cloud of gas

In order for what astronomers call a ‘small galaxy’ to be made, a relatively large and isolated gas cloud is needed.

LARGE GALAXIES 1 A team of gas clouds

Small clouds of gas collapse early on to form the galaxy’s very first stars.

2 The making of stars

Under gravity, the cloud will collapse because there’s not enough pressure from the gas itself to fight against this force pressing it down. Baby stars are made in the fight.

2 A party of stars

These gas clouds and their newly formed stars clump together to make a larger cloud with a party of stellar populations.

3 Forming a disc

Matter spins quickly, causing a flattened disc-like structure. At the centre is a bulge where older first-generation stars can be found. The rest of the disc is teeming with younger stars.

3 Gaseous add-ons

There isn’t much spinning going on during the making of a large galaxy. Instead the merging of nearby gas clouds stops any chances of a disc-like structure forming.

4 A galaxy with arms

Internal processes make the arms and bars found in spiral galaxies. However, if conditions are more favourable, a lenticular galaxy is made instead.

4 A gigantic galaxy

Since most of the gas was mopped up, no more stars can be made. What’s left is a gigantic elliptical galaxy that’s dominated by old stars.