The Boötes Void is a massive spherical region in space approximately 330 million light-years in diameter (accounting for 0.27% of the diameter of the entire Universe) composed of empty space. Also called “The Great Nothing,” this mysterious region resides in the Boötes constellation 700 million light-years away from Earth. Robert Kirshner discovered the Boötes Void in 1981, first reporting it while conducting a survey of galactic redshifts, a study of massive objects moving away from Earth, evidence that our universe continuously expands.

Distributed in a peculiar tube-like manner, the Boötes Void contains a mere 60 identified galaxies, a puzzling phenomenon for such a massive region of space observed for nearly 40 years. The average distance from each galaxy would place one every 10 million light-years, four times the distance of the Andromeda Galaxy from Earth. This greatly contrasts our galactic neighborhood, the Virgo Super Cluster, a much smaller region of space about 110 million light-years in diameter that houses some 2000 plus galaxies including the Milky Way.

Though many voids exist in our universe, this particular one remains one of the largest ever observed. The closest void to our Solar System, ingeniously quipped the Local Void, resides 75 million light-years away, stretching 150 million light-years in diameter, or 45 Mpc (Megaparsecs). The Boötes Void’s 236,000 Mpc3 volume earned it the moniker “the Super Void” or “The Great Void,” and its curious seemingly perfect circular formation around its boundaries mystifies astronomers, while alarming some who consider the possibility that the void represents something sinister. Is this massive void indeed empty, or could some object or phenomenon influence the area, perhaps absorbing all light and particles, creating this dark, empty shroud?

Credits: Powell, Richard Atlas of the Universe 

No widely accepted explanation currently exists for the peculiarity of this region, though it has been theorized that this is just an attribute of cosmic evolution, or the convergence of many smaller voids, similar to how soap bubbles combine to form larger bubbles, leaving flat areas of water.

Devoid of any concrete answers, the existence of the Boötes Void reveals how little our civilization understands about our universe, and remains one of the greatest mysteries of astronomy.

Credit: Andrew Z. Colvin, Zeryphex