Chapter accepted to appear in Planets, Stars and Stellar
Systems, vol 5, ed G. Gilmore, 2011.

astro-ph/1006.4855

For a PDF version of the article, click here.

Rutgers University, Department of Physics & Astronomy,

136 Frelinghuysen Road, Piscataway, NJ 08854-8019

**Abstract:** This chapter reviews theoretical work on the stellar
dynamics of galaxy disks. All the known collective global instabilities are
identified, and their mechanisms described in terms of local wave
mechanics. A detailed discussion of warps and other bending waves is
also given. The structure of bars in galaxies, and their effect on
galaxy evolution, is now reasonably well understood, but there is
still no convincing explanation for their origin and frequency.
Spiral patterns have long presented a special challenge, and ideas and
recent developments are reviewed. Other topics include scattering of
disk stars and the survival of thin disks.

**Table of Contents**

- INTRODUCTION
- PRELIMINARIES
- Relaxation Rate
- Mathematical Formulation
- Orbits
- Resonances
- Wave-Particle Scattering
- Vertical Motion

- LOCAL THEORY OF DENSITY WAVES
- Plane Waves in a Thin Mass Sheet
- Dispersion Relations
- Axisymmetric Stability
- Self-consistent Density Waves
- Group Velocity
- Swing Amplification

- BAR INSTABILITY
- Mechanism for the Bar Mode
- Predicted Stability
- Residual Concerns

- LOP-SIDED MODES
- GROOVE AND EDGE MODES
- SPIRAL STRUCTURE
- Spirals as Global Modes of Smooth Disks
- Recurrent Transients
- Spirals as Responses to Density Fluctuations
- Non-linear Spiral Dynamics
- Spirals in Global N-body Simulations
- A Recurrent Instability Cycle?

- BUCKLING INSTABILITIES AND WARPS
- Local Theory of Bending Waves
- Global Bending Modes
- Simulations of Buckling Modes
- Disks in Halos
- Misaligned Infall
- Warps Driven by Tides

- BARS
- Origin of Bars
- Frequency of Bars
- Structure of Bars
- Gas Flow
- Bar Pattern Speeds
- Bars Within Bars
- Buckling of Bars
- Dynamical Friction on Bars

- SECULAR EVOLUTION WITHIN DISKS
- Heating by Spirals
- Churning by Transient Spirals
- Cloud Scattering
- Black Holes in the Halo
- Discussion

- FRAGILITY OF DISKS
- CONCLUSIONS
- REFERENCES
- APPENDIX: RELAXATION TIME IN SPHEROIDS AND DISKS