Galaxies breathe gas, and when they stop, no more stars form

For most of the history of astronomy, all we could see were stars. We could see them individually, in clusters, in nebulae, and in fuzzy blobs that we thought were clumps of stars but were actually galaxies. The thing is, ...

When did the first exocontinents appear in the universe?

On Earth, continents are likely necessary to support life. Continents "float" on top of the Earth's viscous mantle, and heat from the planet's core keeps the mantle from solidifying and locking the continents into place.

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