What vast underdense region of space lies adjacent to the Local Group?

The vast underdense region adjacent to the Local Group is the Local Void. It is a large cosmic region containing far fewer galaxies than the surrounding filamentary web, though it is not perfectly empty.

The Local Void borders the Local Sheet, the flattened structure of nearby galaxies that includes the Local Group. Astronomers identify such voids by mapping galaxy positions and redshifts: clusters and filaments form dense concentrations, while broad regions show a striking shortage of galaxies.

Brent Tully and Richard Fisher identified the Local Void in 1987. Later studies found that it is not a simple spherical hole; it appears to contain several sectors separated by tenuous bridges or filaments. Its precise dimensions remain uncertain, with estimates spanning tens to hundreds of megaparsecs.

The Local Void is often confused with the proposed KBC Void, also called the Local Hole. The KBC Void is a much larger, disputed underdensity that is described as containing the Milky Way and Local Group. The established nearby structure directly adjacent to the Local Group is the Local Void.