minivoid

Minivoid is a term used in cosmology to denote a relatively small underdense region of the universe within the cosmic web. Compared with large cosmic voids that can span tens of megaparsecs, minivoids are smaller-scale voids, typically a few to tens of megaparsecs in effective radius. They are characterized by density significantly below the mean matter density and by a paucity of galaxies within their boundaries, though low-luminosity galaxies and dark matter may still be present along the rims.

Minivoids arise naturally in the hierarchical growth of structure under gravity. As matter collapses into sheets, filaments, and clusters, voids expand and merge; small underdense regions can survive as distinct minivoids within larger underdense environments. They are identified in simulations and survey data using density reconstructions and void-finding algorithms such as watershed methods or excursion-set approaches, often focusing on regions with low galaxy counts or low halo densities.

Because they sample different environmental conditions than denser regions, minivoids are used to study galaxy formation and evolution in low-density environments, probe the behavior of dark matter and gravity on intermediate scales, and test cosmological models, including properties of dark energy and modified gravity theories. Observationally, they are studied through galaxy redshift surveys and weak gravitational lensing, though their small size makes them challenging to detect and characterize reliably.

Minivoids are related to but distinct from larger cosmic voids; collectively they contribute to the overall texture of the cosmic web and the matter distribution of the universe.