Galaxies themselves occupy a relatively small percentage of the universe's total mass and volume. While galaxies contain a substantial fraction of the visible matter, such as stars and gas, they comprise only about 0.5% of the total mass-energy content of the universe. The majority of the universe is made up of dark energy (approximately 68%) and dark matter (about 27%).
In terms of volume, galaxies are also sparse, as vast regions of space are largely empty. Therefore, while stars and galaxies are crucial components of the universe, their physical volume and mass contribute only a minor fraction compared to the total content of the universe.
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