Book contents
- Frontmatter
- Contents
- Preface
- Introduction
- Part I Idealized homogeneous systems – basic ideas and gentle relaxation
- Part II Infinite inhomogeneous systems – galaxy clustering
- 20 How does matter fill the Universe?
- 21 Gravitational instability of the infinite expanding gas
- 22 Gravitational graininess initiates clustering
- 23 Growth of the two-galaxy correlation function
- 24 The energy and early scope of clustering
- 25 Later evolution of cosmic correlation energies
- 26 N-body simulations
- 27 Evolving spatial distributions
- 28 Evolving velocity distributions
- 29 Short review of basic thermodynamics
- 30 Gravity and thermodynamics
- 31 Gravithermodynamic instability
- 32 Thermodynamics and galaxy clustering; ξ(r)∝r-2
- 33 Efficiency of gravitational clustering
- 34 Non-linear theory of high order correlations
- 35 Problems and extensions
- 36 Bibliography
- Part III Finite spherical systems – clusters of galaxies, galactic nuclei, globular clusters
- Part IV Finite flattened systems – galaxies
- Index
22 - Gravitational graininess initiates clustering
Published online by Cambridge University Press: 05 July 2011
- Frontmatter
- Contents
- Preface
- Introduction
- Part I Idealized homogeneous systems – basic ideas and gentle relaxation
- Part II Infinite inhomogeneous systems – galaxy clustering
- 20 How does matter fill the Universe?
- 21 Gravitational instability of the infinite expanding gas
- 22 Gravitational graininess initiates clustering
- 23 Growth of the two-galaxy correlation function
- 24 The energy and early scope of clustering
- 25 Later evolution of cosmic correlation energies
- 26 N-body simulations
- 27 Evolving spatial distributions
- 28 Evolving velocity distributions
- 29 Short review of basic thermodynamics
- 30 Gravity and thermodynamics
- 31 Gravithermodynamic instability
- 32 Thermodynamics and galaxy clustering; ξ(r)∝r-2
- 33 Efficiency of gravitational clustering
- 34 Non-linear theory of high order correlations
- 35 Problems and extensions
- 36 Bibliography
- Part III Finite spherical systems – clusters of galaxies, galactic nuclei, globular clusters
- Part IV Finite flattened systems – galaxies
- Index
Summary
The single atoms each to other tend,
Attract, attracted to, the next in place
Form'd and impell'd its neighbour to embrace.
Alexander PopeParallel to the comparison developed in Sections 15 and 16, we next turn to new phenomena which graininess introduces into the growth of perturbations. In a major application of this theory, the grains are galaxies. Despite our ignorance of their formation, we can ask how gravity causes galaxies to cluster. Does the clustering we expect explain what we see?
The simplest result can even be anticipated from our analysis in the last section. Consider a gas of galaxies. Let it be uniform except for √N fluctuations. If we treat it, for a moment, as a fluid, then the growth rate of perturbations in a standard cosmology, ρ1(t)∝ R(t)∝t⅔, tells us that observed clusters with ~ 104 galaxies should be able to form easily starting at redshifts of 102 - 103. So galaxy clustering promises to be more understandable than galaxy formation, although it still has its mysteries.
Realizing the relative ease of galaxy clustering, it becomes natural to push the process back a step. Could galaxies themselves be the result of an earlier clustering? Suppose that isothermal perturbations of the Jeans mass at decoupling, ~ 106 M⊙, started (somehow) with large amplitudes and formed bound systems. It would take about 104 of these to form a small galaxy.
- Type
- Chapter
- Information
- Gravitational Physics of Stellar and Galactic Systems , pp. 158 - 162Publisher: Cambridge University PressPrint publication year: 1985