Galaxies are thought to begin as small clouds of stars and dust swirling through space. As other clouds get close, gravity sends these objects careening into one another and knits them into larger spinning packs.

How are galaxies made?

Galaxies are composed of stars, dust and dark matter, all held together by gravity. Astronomers aren't certain exactly how galaxies formed. ... Some astronomers think that gravity pulled dust and gas together to form individual stars, and those stars drew closer together into collections that ultimately became galaxies.

When and how did galaxies form?

Based on cosmic microwave background data, astronomers think matter coalesced when the universe cooled and became “transparent” 380,000 years after the Big Bang. And according to recent studies, structures like stars and galaxies formed as early as 200 million years after the Big Bang.