Why do galaxies spin?

What caused the rotation of galaxies, and do they all do it?


Asked by Andy Meadows

It is said that everything spins in the Universe – from galaxies to stars to planets. But why do galaxies rotate?

In the early stages of the Universe, clouds of gas came together to form the stars. These stars were then gravitationally attracted to each other to create gigantic clusters of stars enshrouded in clouds of gas. Eventually these groupings of stars come together through the attraction of gravity and together they start to spin around a common centre of mass. Picking up speed, the rotation squashes the clusters of stars flat forming a disk with a bulge at the centre.

This spinning of galaxies continues even after their formation. Our Milky Way galaxy is one of these spinning structures and its entire disc of stars, gas and dust is rotating at around 168 miles per second. Due to our Galaxy’s rotation, our Solar System appears to orbit the galaxy every 225 million years – the last time we were in the same place in our orbit, dinosaurs were just starting to appear on the Earth. All galaxies spin whatever their type or size.

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