Minivoids

Minivoids are the smallest underdense regions within the large-scale structure of the universe. They are low-density spaces surrounded by higher-density filaments, walls, and clusters, and may host few or no galaxies. Minivoids are considered the small-scale counterparts to larger cosmic voids and can be embedded within larger underdense regions or appear at the edges of cosmic structures.

In cosmology, minivoids are identified through analysis of galaxy surveys and cosmological simulations. Density-based criteria and void-finding algorithms locate local minima in the density field and delineate their boundaries. Methods such as watershed approaches and Voronoi tessellation-based techniques are commonly used, often adapted to detect smaller-scale voids. Observationally, challenges include sparse sampling, survey geometry, and redshift-space distortions, which can affect the detection and characterization of tiny underdense regions.

Typical properties of minivoids include irregular, non-spherical shapes and densities well below the mean cosmic density, though they are not completely empty. Internal velocity fields tend to exhibit outflow patterns as matter evacuates the region, and the boundaries are often defined by surrounding walls and filaments that concentrate matter.

Formation and significance: minivoids arise from primordial density fluctuations evolved under gravity. They provide a testing ground for models of dark matter, dark energy, and gravity on small scales, and they help illuminate environmental effects on galaxy formation and evolution. By studying minivoids, researchers gain insight into how matter distributes itself in the cosmic web and how small-scale structure interacts with the broader universe.