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Dynamics of elliptical galaxies.

Science (New York, N.Y.)

|March 26, 1993

Summary

Elliptical galaxies are now understood to be triaxial, not flattened, due to slow rotation. This triaxial shape is stable, supported by conserved quantities in galactic dynamics.

Area of Science:

Astronomy and Astrophysics
Galactic Dynamics
Galaxy Formation

Background:

Historically, elliptical galaxies were modeled as rotationally flattened systems, akin to stars.
Newer findings reveal slow rotation in elliptical galaxies, challenging previous structural and dynamic assumptions.
This discrepancy necessitates a revised understanding of their internal mechanics.

Purpose of the Study:

To re-evaluate the structural and dynamic models of elliptical galaxies.
To explain the observed slow rotation rates in elliptical galaxies.
To investigate the stability and formation mechanisms of these galactic systems.

Main Methods:

Theoretical modeling of self-consistent triaxial equilibria.
Analysis of conserved quantities (integrals of motion) in non-rotationally symmetric potentials.

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Review of observational evidence for galaxy shapes and central mass concentrations.

Main Results:

Elliptical galaxies are characterized by fully triaxial shapes, not flattened structures.
Self-consistent triaxial equilibria are long-lived, supported by integrals of motion.
Instabilities in some equilibria may explain the limited axis ratios (≤3:1) observed in elliptical galaxies.
Evidence suggests central mass concentrations, potentially massive black holes, exist in some elliptical galaxies.
Recent observations indicate elliptical galaxy formation via mergers of spiral galaxies.

Conclusions:

The triaxial model provides a more accurate representation of elliptical galaxy dynamics.
Galactic potential symmetries and conserved quantities are crucial for stable triaxial equilibria.
Galaxy mergers are a significant pathway for the formation of elliptical galaxies.