The first dwarf galaxies to form in the universe sabotaged their own growth and that of their siblings by ionizing surrounding hydrogen gas. Early galaxies were small, containing only 100 million solar masses of material. Later galaxies required at least 10 billion solar masses to be assembled. This artist's conception shows a collection of hot, blue stars comprising an early dwarf galaxy surrounded by red hydrogen gas. Credit: David A. Aguilar (CfA)
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