The
large scale structure (LSS) of the universe refers to the organization and distribution of matter on scales much larger than individual galaxies. It encompasses the arrangement of
galaxy clusters, superclusters, voids, filaments, and walls. These structures form a cosmic web that spans hundreds of millions of light-years, offering critical insights into the universe’s formation and evolution.
Observing the large scale structure requires extensive surveys of the sky. Instruments like the Sloan Digital Sky Survey (
SDSS) and the Dark Energy Survey (
DES) have mapped the positions of millions of galaxies, enabling astronomers to create detailed 3D maps of the universe. Techniques such as redshift measurements help determine the distances to these galaxies, providing a clearer picture of their distribution in space.
The
cosmic web is the large-scale structure of the universe, composed of interconnected filaments of dark matter and galaxies, interspersed with vast voids. It resembles a web-like pattern and is a result of gravitational interactions over billions of years. The cosmic web's structure is heavily influenced by the initial conditions of the universe and the subsequent growth of
cosmic perturbations.
Role of Dark Matter
Dark matter plays a crucial role in the formation and evolution of the large scale structure. It constitutes about 27% of the universe's mass-energy content and acts as the gravitational scaffolding for normal matter (baryonic matter) to clump together and form galaxies and larger structures. Simulations of the universe's evolution, such as the
Millennium Simulation, show how dark matter halos attract baryonic matter, leading to the formation of galaxies and the cosmic web.
Voids are vast, nearly empty regions of space that contain very few galaxies, whereas
filaments are elongated structures that connect clusters of galaxies. Voids can be tens to hundreds of millions of light-years across and are among the largest structures in the universe. Filaments act as the "skeleton" of the large scale structure, guiding the formation and distribution of galaxies along their lengths.
Baryon Acoustic Oscillations (BAO) are regular, periodic fluctuations in the density of the visible baryonic matter of the universe. These oscillations left an imprint on the distribution of galaxies and can be observed as a characteristic scale in the large scale structure. BAO serves as a "standard ruler" for cosmological measurements, helping to determine the expansion rate of the universe and the nature of
dark energy.
Gravity is the primary force shaping the large scale structure. Small initial density fluctuations in the early universe grew under gravitational attraction, leading to the formation of a hierarchical structure: small objects like stars and galaxies formed first, followed by galaxy groups, clusters, and eventually superclusters. This hierarchical formation is described by the
Lambda Cold Dark Matter (ΛCDM) model, which is the prevailing cosmological model.
Future Research and Observations
Future research aims to refine our understanding of the large scale structure with more detailed surveys and advanced simulations. Upcoming missions like the
Euclid Space Telescope and the
Vera C. Rubin Observatory will provide unprecedented data on the distribution of galaxies and dark matter. These observations will help to test cosmological models, explore the nature of dark energy, and improve our understanding of the universe's large scale structure.
