# Why do galaxies rotate?

> Galaxies spin due to conservation of angular momentum from early cosmic collisions.
- Title: Why do galaxies rotate? · The Conversation | Shortify
- Summary: Galaxies spin due to conservation of angular momentum from early cosmic collisions. Galaxies rotate because collisions during formation conserved angular…
- Keywords: galaxies, angular momentum, conservation of angular momentum, cosmic collisions, spiral galaxies, dark matter, galactic formation, science, ideas, rotate, The Conversation
- Source: The Conversation — https://theconversation.com/why-do-galaxies-rotate-291508
- Author: Edwin Alexani
- Read time: 1 min
- Topics: galaxies, angular momentum, conservation of angular momentum, cosmic collisions, spiral galaxies, dark matter, galactic formation, science, ideas
## Why do galaxies rotate?
Galaxies spin because early cosmic collisions conserved angular momentum.
## Spinning in space
Spinning is common in space, from Earth to the Milky Way and many objects.
## Angular momentum
The amount of spin an object has depends on its mass and how mass is distributed around its center of mass.
## Conservation of angular momentum
Pulling mass closer to the center of mass increases spinning speed, as seen in figure skaters and chairs.
## Galaxy formation
Galaxies form from gas and dust clouds colliding, which often start spinning due to off-center approaches.
## Dark matter's role
Dark matter helps pull gas and dust clouds together through gravity, aiding galaxy formation.
## Spiral galaxies
Spiral galaxies have a flat disk with spiral arms and a central bulge, where most matter rotates in the same direction.
## Elliptical galaxies
Elliptical galaxies have few gas and dust, with stars orbiting the center but no organized rotation.
## Galaxy rotation types
Irregular galaxies have general rotation but some objects do not follow it, while others spin more organized.
## Key takeaway

Galaxies rotate because collisions during formation conserved angular momentum.