Large-Scale Structure of Universe
The Large-Scale Structure (LSS) of the universe refers to the web-like spatial distribution of matter — including galaxies, galaxy clusters, filaments, walls, and voids — on scales from tens to hundreds of megaparsecs. Driven by gravitational collapse of primordial density fluctuations seeded during inflation, this cosmic web is the largest organized structure in existence. Mapping and modeling the LSS provides critical tests of cosmological models, measurements of dark matter and dark energy densities, and constraints on the neutrino mass.
Components of the Cosmic Large-Scale Structure
| Structure | Typical Scale | Density Contrast | Example |
|---|---|---|---|
| Galaxy cluster | 1–10 Mpc | δ ≈ 200–1000 | Virgo Cluster |
| Filament | 10–100 Mpc | δ ≈ 5–20 | Perseus-Pisces filament |
| Sheet / Wall | 50–200 Mpc | δ ≈ 2–10 | Great Wall (CfA2) |
| Void | 10–100 Mpc | δ ≈ −0.9 to −1 | Boötes Void |
| Supercluster | 100–500 Mpc | δ ≈ 1–5 | Laniakea Supercluster |
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Related Terms
Epoch of Reionization
The Epoch of Reionization (EoR) is a pivotal phase in cosmic history, spanning roughly 150 million to 1 billion years after the Big Bang (redshifts z ≈ 6–20), during which the first stars and quasars emitted enough ultraviolet radiation to ionize the neutral hydrogen that pervaded the universe after recombination. This process transformed the intergalactic medium from a neutral, opaque state back into the fully ionized, transparent plasma we observe today. Understanding the EoR is one of the central goals of modern observational cosmology, as it marks the emergence of the large-scale structure of the universe and the first generation of galaxies.
Dark Matter
Dark matter is a hypothetical form of matter that does not interact with the electromagnetic force, making it invisible to the entire electromagnetic spectrum, yet its existence is inferred from its gravitational effects on visible matter, radiation, and the large-scale structure of the universe. It is estimated to constitute approximately 27% of the total mass-energy content of the universe, compared to only 5% for ordinary baryonic matter. Leading candidates include Weakly Interacting Massive Particles (WIMPs), axions, and sterile neutrinos, though no direct detection has been confirmed as of 2025.
Cosmic Microwave Background
The Cosmic Microwave Background (CMB) is the thermal electromagnetic radiation permeating the entire observable universe, representing the afterglow of light released approximately 380,000 years after the Big Bang when the universe cooled enough for protons and electrons to combine into neutral hydrogen atoms. It is observed today as a nearly uniform blackbody radiation at a temperature of approximately 2.725 K, with tiny temperature fluctuations of about 1 part in 100,000 that encode the seeds of large-scale cosmic structure. The CMB is considered one of the strongest pieces of evidence for the Big Bang model and provides precise measurements of cosmological parameters.
From Latin structura (meaning "arrangement" or "building"), combined with "large-scale" indicating spatial extents far beyond individual galaxies. The term became standard in cosmological literature in the 1980s following pioneering redshift surveys like the CfA Survey.