Britannica Sources used in this answer

When did the first stars and galaxies begin to form?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Britannica editor Erik Gregersen, a white man wearing glasses, holds a microphone in front of a galaxy background. Displayed above him are the phrases: Ask an Editor, and How old is the universe? — Universe And how do you even start to answer this question?

According to the big-bang theory, the first stars and galaxies began to form a few hundred million years after the initial expansion of the universe, which occurred approximately 13.8 billion years ago.1

Following the big bang, the universe expanded and cooled, allowing subatomic particles and eventually atoms to form. Under the influence of gravity, these atoms clumped together to create the first structures. Observations from the Hubble Space Telescope confirm that when the universe was only a few hundred million years old, it was populated by small, irregular objects that served as the building blocks for larger galaxies. It is widely believed that most galaxies began to form during this same epoch as matter condensed.123