How do galaxies form and grow over time?
Quick Answer
Small clumps of matter formed first, then gravity pulled gas together into stars and merged smaller systems into larger galaxies. This hierarchical growth continues today through mergers and gas accretion.
The Full Story
In the early universe, tiny density fluctuations grew under gravity into dark-matter halos, which attracted gas. As gas cooled, stars began to form, creating the earliest galaxies. Over billions of years, galaxies grew by merging with one another and by drawing in more gas from their surroundings. Computer simulations and deep telescope surveys show this hierarchical process in action. The Milky Way itself has absorbed smaller galaxies and still interacts with neighbors like the Sagittarius dwarf galaxy.
Key Facts
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Suggested video title for this topic:
"How tiny cosmic seeds became giant galaxies"
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