Uncovering the Mysteries of Cosmic Voids: A Historical Overview.

TL;DR
Astronomers discovered the first cosmic void in the early 1970s, which was a blank space devoid of galaxies almost 20 megaparsec, or 65 million light-years, across. This discovery was made after the realization that there was more in the Universe than mere galaxies and clusters, and that there was something larger - the supercluster. With the advancement of technology and techniques, astronomers were able to map the heavens and understand the large-scale structure of the Universe, including the clumping of galaxies into clusters and clusters into superclusters.
A Brief History of the Discovery of Cosmic Voids Universe Today
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