Structure of the universe
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Structure of the Universe: An Overview
Formation and Evolution of Cosmic Structures
Primordial Ripples and Gravitational Amplification
The large-scale structure of the universe is believed to have originated from weak ripples in the primordial soup shortly after the Big Bang. These ripples, initially small density fluctuations, were amplified over billions of years by gravitational forces, leading to the formation of dense regions of dark matter where galaxies eventually formed1. This process has been extensively modeled through computer simulations, which align well with observational data from as early as 400,000 years after the Big Bang1.
Cold Dark Matter Model
The cold dark matter (CDM) model is the leading theoretical framework for understanding the formation of cosmic structures. According to this model, structures in the universe grow hierarchically through gravitational instability, starting from small initial fluctuations2 4. This model, combined with the theory of cosmic inflation, provides a robust explanation for the initial conditions of structure formation and predicts the hierarchical growth of structures2.
Mixed Dark Matter Models
While the CDM model has been successful, it has faced challenges in explaining certain observations, such as the quiet velocity field of galaxies and large-scale structures. Mixed dark matter models, which include both cold and hot dark matter components, have been proposed to address these issues. These models suggest that a combination of CDM and hot dark matter (HDM), such as massive neutrinos, can better match the observed large-scale power and the cosmic microwave background fluctuations10.
Observational Constraints and Theoretical Models
Power Spectrum of Primordial Density Fluctuations
Observations have accumulated enough data to constrain the power spectrum of primordial density fluctuations over a wide range of scales. This has allowed researchers to test and refine various cosmogonical theories, potentially determining the most accurate models for the origin of large-scale cosmic structures3.
Nonlinear Growth and Phase Correlations
The evolution of cosmic structures involves both linear and nonlinear processes. Initially, small overdense regions grow independently, but as they accumulate more mass, they begin to interact in complex, nonlinear ways. Recent studies have developed methods to quantify these nonlinear interactions, revealing how they contribute to the formation of filaments, sheets, and clusters of galaxies7.
Fractal and Multifractal Nature of the Universe
Long-Range Correlations and Fractal Structures
Re-evaluations of experimental data using modern statistical mechanics have shown that the universe exhibits long-range, fractal correlations up to the observational limits. This fractal nature implies that the distribution of visible matter is highly non-analytic, challenging previous assumptions of homogeneity and finite correlation lengths8. The multifractal properties of the universe also help explain phenomena such as luminosity segregation and the richness-clustering relation8.
Conclusion
The structure of the universe is a complex and dynamic tapestry shaped by primordial fluctuations, gravitational forces, and the interplay of dark matter components. While the cold dark matter model remains a cornerstone of our understanding, mixed dark matter models and advanced statistical methods continue to refine our knowledge. Observational data and computer simulations play a crucial role in testing and validating these theories, offering deeper insights into the cosmic evolution from the Big Bang to the present day.
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Most relevant research papers on this topic
The large-scale structure of the Universe
The rich tapestry of present-day cosmic structure arose during the first instants of creation, when weak ripples were imposed on the otherwise uniform and rapidly expanding primordial soup, and over 14 billion years, gravitational forces amplified these ripples to enormous proportions, producing ever-growing concentrations of dark matter in
Highly CitedSimulations of the formation, evolution and clustering of galaxies and quasars
This study simulates the growth of dark matter structure and galaxies and quasars, revealing distortions in the low-redshift galaxy distribution, which can constrain the nature of dark energy with future galaxy surveys.
Highly CitedLarge-scale structure in the Universe
Large-scale cosmic structures are influenced by various observations, and future observations should be able to determine the power spectrum of primordial density fluctuations.
Highly CitedLarge‐Scale Structure in the Universe
The 1980s saw a shift in focus from H and qo to the frothy distribution of galaxies and coherent motions, revealing the nature and distribution of dark matter and the processes that drafted the complex galaxy distribution.
Studies on the Structure of the Universe
A VERY interesting publication has recently been issued by Mr. Stratonoff, of the Russian Observatory at Tachkent, on the structure of the universe, a problem which has a fascination of its own for most readers quite apart from any real progress which may be made towards its solution.
Cosmic strings and the large-scale structure of the Universe.
Cosmic strings can explain the large-scale structure of the Universe, including voids and filaments, and predict the presence of pointlike structures with masses >10/sup 7/M near larger galaxies.
Highly CitedCharacterizing the nonlinear growth of large-scale structure in the Universe
This study presents a method to quantitatively reveal phase information in cosmic structure, revealing the formation of filaments, sheets, and clusters of galaxies by nonlinear collapse.
The fractal structure of the universe
The universe's visible matter distribution is fractal and multifractal up to current observational limits, with no evidence for homogenization and no simple average density can be defined.
Highly CitedLarge-scale structure in a universe with mixed hot and cold dark matter
A mixed dark matter model with 70% cold and 30% hot matter can explain observed large-scale structure formation and cosmic density differences on small and large scales.
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