Large-scale structure and cosmic web

Big Ring

The Big Ring is a ring-shaped large-scale structure of galaxies about 1.3 billion light-years in diameter, found near Boötes at redshift 0.8 and reported in 2024 by Alexia Lopez.

Cosmic homogeneity scale

The cosmic homogeneity scale is the distance above which galaxies stop clustering fractally and become statistically uniform, typically measured at about 70 h⁻¹ Mpc in galaxy surveys.

CosmicFlows

CosmicFlows is a series of catalogs of galaxy distances and peculiar velocities, led by R. Brent Tully at the University of Hawaiʻi, running from Cosmicflows-1 (2008) to Cosmicflows-4 (2023).

Cosmological simulation

A cosmological simulation is a computer model evolving a volume of the Universe from shortly after the Big Bang to the present, tracking the gravitational growth of cosmic structure.

Effective field theory of large-scale structure

The effective field theory of large-scale structure (EFTofLSS) is a cosmological framework that predicts matter and galaxy clustering by treating dark matter as an effective fluid.

Galaxy formation and evolution

Galaxy formation and evolution is the branch of astrophysics that studies how galaxies arose from primordial density fluctuations in dark matter and gas and changed across 13.8 billion years.

Giant Arc (large-scale structure)

The Giant Arc is a proposed large-scale structure of galaxies, clusters, and gas spanning about 1 gigaparsec, reported in 2021 and seen at redshift 0.8.

Gravitational collapse

Gravitational collapse is the contraction of a region of matter under its own gravity when supporting pressure is insufficient, first analyzed by James Jeans in 1902.

Growth index (cosmology)

The growth index is a cosmological parameter, written γ, that summarizes how fast cosmic structures grow; it is about 0.55 in general relativity and differs in modified gravity.

Halo bias

Halo bias is the cosmological relation between the spatial distribution of dark matter haloes and the dark matter density field, quantifying how haloes cluster more strongly than matter itself.

Halo mass function

The halo mass function (HMF) is the comoving number density of dark matter halos per unit mass, a central prediction of structure formation models used to constrain cosmological parameters.

Halo occupation distribution

The halo occupation distribution (HOD) is a statistical model in cosmology giving the probability that a dark matter halo of a given mass contains a given number of galaxies.

Hierarchical structure formation

Hierarchical structure formation is the cosmological model in which small structures such as dwarf galaxies and dark matter halos form first, later merging into larger galaxies and clusters.

Hubble bubble hypothesis

The Hubble bubble hypothesis proposes that the Milky Way sits inside a large underdense region whose outflow makes the locally measured expansion rate of the universe appear higher.

Illustris is a suite of large cosmological hydrodynamical simulations of galaxy formation, run with the moving-mesh code Arepo and completed in late 2013, producing about 40,000 well-resolved galaxies in a box 106.5 megaparsecs on a side.

KBC void

The KBC void, also called the Local Hole, is a proposed region around the Local Group about 20 percent less dense than the cosmic average, extending roughly 300 megaparsecs.

Large-scale structure of the universe

The large-scale structure of the universe, known as the cosmic web, is the pattern in which galaxies cluster along filaments and sheets surrounding vast voids.

List of largest cosmic structures

The list of largest cosmic structures covers galaxy walls, large quasar groups, and superstructures spanning hundreds of megaparsecs, from the Sloan Great Wall to Quipu.

Lyman-alpha forest

The Lyman-alpha forest is the dense set of absorption lines from neutral hydrogen in the spectra of distant quasars, tracing the intergalactic medium along the line of sight.

Millennium Simulation

The Millennium Simulation, also called the Millennium Run, is a 2004 computer simulation of dark matter structure growth, run by the Virgo Consortium and published in 2005.

Quipu (cosmic structure)

Quipu, named for the Incan knotted cords, is a filamentary superstructure of galaxy clusters identified in 2025 as the largest found in its survey, about 1.3 billion light-years long with a mass of 200 quadrillion Suns.

Redshift-space distortions

Redshift-space distortions (RSD) are anisotropic distortions of the observed galaxy distribution arising from peculiar velocities: the Kaiser effect on large scales and Fingers of God in clusters.

S8 tension

The S8 tension is a cosmological discrepancy: the cosmic microwave background implies a higher amplitude of matter clustering than weak gravitational lensing and galaxy surveys measure at low redshift.

Sloan Great Wall

The Sloan Great Wall is a vast filament of galaxies about a billion light-years from Earth, identified in 2003 by J. Richard Gott III and Mario Jurić as then the largest known structure.

Sound horizon

The sound horizon is the distance sound waves traveled in the primordial plasma before recombination, about 147 Mpc, surviving as the baryon acoustic oscillation scale.

Void (astronomy)

A cosmic void, or supervoid, is a large underdense region of the universe, typically 5 to 100 megaparsecs across, bounded by the filaments of the cosmic web.

Void galaxy

A void galaxy is a galaxy inside a cosmic void, an underdense region of the Universe. They are blue, low-mass, gas-rich galaxies that evolve slowly.

Warm-hot intergalactic medium

The warm-hot intergalactic medium (WHIM) is diffuse, highly ionized gas at 10^5 to 10^7 K in cosmic-web filaments, proposed to hold half the universe's missing ordinary matter.