Astrophysics & Particle Physics-APPC 2026

Cosmic voids are huge, underdense areas of space in the universe that have much fewer galaxies, stars, and matter than typical. They are a necessary component of the cosmic web, the huge galaxy, cluster, filament, and void network that constitutes the universe's large-scale structure. Spanning tens to hundreds of millions of light-years in diameter, voids dominate the cosmic volume, yet contain a small percentage of the total matter.They are not necessarily empty space—within them exist tenuous distributions of galaxies, dark matter, and intergalactic gas.

Their low-density context makes them special testing grounds for cosmological theory. Since voids grow more rapidly than the typical universe, voids are sensitive to dark energy properties and to cosmic acceleration dynamics. Through the investigation of cosmic voids' shapes, sizes, and distributions, scientists obtain strong information on the underlying physics of the universe.Cosmic voids also complement the other cosmological probes such as galaxy clustering, gravitational lensing, and baryon acoustic oscillations (BAO). The signature of voids on the cosmic microwave background (CMB), the Integrated Sachs-Wolfe effect, is another evidence for the dark energy's effect. Big redshift surveys such as the Sloan Digital Sky Survey (SDSS) and the Dark Energy Survey (DES) have charted thousands of voids, making three-dimensional maps of the structure of the universe.Voids contain galaxies that live in these underdense regions, providing insight into how galaxies form and evolve with little external impact.

These galaxies are typically small, lone, and gas-rich, so they are particularly useful for studying star formation under unspoiled conditions.In cosmology, supervoids—enormous structures with lengths of hundreds of millions of light-years—are of special interest because supervoids can influence CMB anomalies and cosmic flows at large scales.On the whole, cosmic voids are huge, low-density spaces that tell us as much about the universe as do the material-filled objects surrounding them. By observing them, astronomers can explore dark matter, dark energy, and the large-scale structure of the universe, gaining a better understanding of the universe's hidden infrastructure.