Book contents
- Frontmatter
- Contents
- Preface
- Introduction
- Part I Idealized homogeneous systems – basic ideas and gentle relaxation
- Part II Infinite inhomogeneous systems – galaxy clustering
- Part III Finite spherical systems – clusters of galaxies, galactic nuclei, globular clusters
- Part IV Finite flattened systems – galaxies
- 56 Observed dynamics of galaxies
- 57 Kinematics of motion
- 58 Transfer of angular momentum
- 59 Rotation curves and galaxy mass
- 60 Orbits and third integrals
- 61 Axisymmetric and bar instabilities
- 62 Spiral instabilities
- 63 Triaxial and irregular systems
- 64 Gravitational shocks
- 65 Passing–merging
- 66 Problems and extensions
- 67 Unanswered questions
- 68 Bibliography
- Index
63 - Triaxial and irregular systems
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
- Part III Finite spherical systems – clusters of galaxies, galactic nuclei, globular clusters
- Part IV Finite flattened systems – galaxies
- 56 Observed dynamics of galaxies
- 57 Kinematics of motion
- 58 Transfer of angular momentum
- 59 Rotation curves and galaxy mass
- 60 Orbits and third integrals
- 61 Axisymmetric and bar instabilities
- 62 Spiral instabilities
- 63 Triaxial and irregular systems
- 64 Gravitational shocks
- 65 Passing–merging
- 66 Problems and extensions
- 67 Unanswered questions
- 68 Bibliography
- Index
Summary
And enterprises of great pitch and moment
With this regard their currents turn awry
ShakespeareIntroduction – spinning polytropes
In our continued progression toward decreasing symmetry, we now arrive at the most individualistic systems of all. Previously we discussed flattened systems which were mainly thin disks. But those cannot represent the large observed class of elliptical galaxies. Ellipticals show moderate rotation, and as a result they have less global coherence than either spirals or spherical non-rotating systems. Pressure, rotation and internal currents all combine to determine a variety of structures and shapes.
Historically, some of the great eighteenth, nineteenth- and early-twentieth century mathematicians began to develop this subject by rigorously analyzing certain simple, highly specialized cases. Magnificent though these achievements were – and they often led to important mathematical insights – they also raised the stature of certain models so high that their astronomical importance became greatly exaggerated. All these models were built from uniform, incompressible fluids. The first of these non-spherical self-gravitating models were Maclaurin's (mid-eighteenth- century) spheroids. They have a stately uniform rotation, with no internal motions. Gravity is balanced by incompressibility and rotation. This balance can exist only for certain values of the spin ratio (58.1), nearly equal to unity. Two types of Maclaurin spheroids, with small and large eccentricities, are possible equilibrium figures.
So simple and satisfying seemed Maclaurin's results, that nearly a century went by before Jacobi realized that other equilibrium figures exist.
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- Gravitational Physics of Stellar and Galactic Systems , pp. 456 - 462Publisher: Cambridge University PressPrint publication year: 1985