The Boötes Void is a massive 'Great Nothing' spanning 330 million light-years that is almost entirely empty.

The Boötes Void was discovered in 1981 by astronomer Robert Kirshner and his colleagues during a survey of galactic redshifts. Located in the vicinity of the Boötes constellation, it is approximately 700 million light-years away from Earth. This spherical region of space has a diameter of nearly 330 million light-years, making up about 0.27% of the diameter of the observable universe.In a standard distribution of matter, a volume of this magnitude should contain roughly 2,000 to 10,000 galaxies depending on the density of the surrounding cosmic web. However, only 60 galaxies have been confirmed within its boundaries to date. These internal galaxies are often arranged in a loose tube shape that likely represents the remnants of a structure swallowed by the void's expansion.The formation of such a 'supervoid' is explained by the hierarchical model of cosmic structure. Small voids, which are regions with lower-than-average density, expand faster than the rest of the universe. As they grow, they collide and merge with one another, pushing matter toward the edges to form dense filaments and clusters.The Boötes Void is so vast that it challenges some aspects of the Lambda CDM model of cosmology. If a traveler were positioned in the center of the void, the night sky would appear completely black in every direction. It would have taken the development of high-sensitivity radio telescopes and advanced long-exposure photography in the mid-20th century for humanity to realize the universe contained anything beyond our own galaxy.