bottom-up structure formation
diseš-e sâxtâr az pâyin bé bâlâ
Fr.: formation des structures du bas vers le haut
A → structure formation scenario in which small galaxies form first, and larger structures are then formed in due course. Contrary to → top-down structure formation.
hierarchical structure formation
diseš-e sâxtâr-e pâygâni
Fr.: formation de structures hiérarchiques
A cosmological → structure formation model in which the smallest gravitationally bound structures (→ quasars and galaxies) form first, followed by → groups, → galaxy clusters, and → superclusters of galaxies.
→ hierarchical; → structure; → formation.
Fr.: formation des structures
The study of the processes that gave rise to the apparition of matter concentrations,
such as → superclusters of galaxies,
→ galaxy clusters, and galaxies, in a homogeneous
→ expanding Universe.
Cosmic structures are believed to result from → density fluctuations
that existed in the → early Universe
before radiation and matter decoupled (→ decoupling era
or → recombination era). Initial
→ quantum fluctuations in the → inflaton field
were expanded by → inflation. Inflation amplified
them up to scales that correspond to those of galaxy clusters and beyond.
Generally, a model of structure formation includes three main ingredients: 1) background
cosmology, 2) model for fluctuation generation, and 3) types of
→ dark matter.
top-down structure formation
diseš-e sâxtâr az bâlâ bé pâyin
Fr.: formation des structures du haut vers le bas
A cosmological model of → structure formation in which larger structures, such as galaxy → superclusters or perhaps even the vast → filaments and → voids, form earlier and then they fragment into smaller structures such as individual galaxies. Opposite of → bottom-up structure formation.