Why does the universe contain so many galaxies of different sizes?
Quick Answer
Galaxies grow by collapsing gas and by merging with smaller galaxies over billions of years. Different environments and histories produce dwarfs, spirals, ellipticals, and irregulars.
The Full Story
After the Big Bang, matter was distributed unevenly, and slightly denser regions grew faster under gravity. Some regions accumulated enough gas to form small dwarf galaxies, while others kept growing by accreting matter and merging with neighbors. Over time, repeated mergers can build large elliptical galaxies, while quiet gas-rich systems can remain spirals. The Hubble Space Telescope and large sky surveys have shown that galaxy shapes and sizes reflect their formation history. In cosmic terms, galaxies are still evolving today.
Key Facts
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