Galaxy
Galaxies are assemblies of stars that may often have a black hole at their center. There may contain anywhere between 10 million to 100 trillion stars.
We can, in theory, observe about 100 billion galaxies. Galaxies have been observed to exist in various shapes: elliptical, spiral, and lens shaped, and irregular. Galaxies usually form into clusters. Clusters are moving apart due to the expansion of the universe. There may be about 500 billion galaxies in the universe.
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