Publication Date

1994

Journal or Book Title

ASTROPHYSICAL JOURNAL

Abstract

A perturber may excite a coherent mode in a star cluster or galaxy. If the stellar system is stable, it is commonly assumed that such a mode will be strongly damped and therefore of little practical consequence other than redistributing momentum and energy deposited by the perturber. This paper demonstrates that this assumption is false; weakly damped modes exist and may persist long enough to have observable consequences. To do this, a method for investigating the dispersion relation for spherical stellar systems and for locating weakly damped modes in particular is developed and applied to King models of varying concentration. This leads to the following remarkable result: King models exhibit very weakly damped m = 1 modes over a wide range of concentration (0.67 ≤ c ≤ 1.5 have been examined). The predicted damping time is tens to hundreds of crossing times. This mode causes the peak density to shift from and slowly revolve about the initial center. The existence of the mode is supported by n-body simulation. Higher order modes and possible astronomical consequences are discussed. Weakly damped modes, for example, may provide a natural explanation for observed discrepancies between density and kinematic centers in galaxies, the location of velocity cusps due to massive black holes, and m = 1 disturbances of disks embedded in massive halos. Gravitational shocking may excite the m = 1 mode in globular clusters, which could modify their subsequent evolution and displace the positions of exotic remnants.

Comments

This is a pre-published version which is collected from arXiv link.

DOI

https://doi.org/10.1086/173665

Pages

481-490

Volume

421

Issue

2

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