Galactic bar: normal mode of the stellar disk or superposition of transient spirals?

TL;DR

This paper investigates whether galactic bars form mainly through stable normal modes or as a superposition of transient spirals, using N-body simulations and linear theory to analyze their development.

Contribution

It demonstrates that galactic bars can develop as a result of unstable normal modes, aligning simulation results with linear perturbation theory, and discusses the role of transient spirals.

Findings

Bar formation aligns with unstable normal modes

Pattern speed and growth rate match linear theory

Transient spirals influence nonlinear evolution

Abstract

Several mechanisms of bar formation in stellar galactic disks are considered, including Toomre swing amplification and normal mode approach. On example of the well-known model of Kuzmin--Toomre using N-body simulations it was shown that the stellar bar is developed as a result of the evolution of an unstable normal mode. The pattern speed and the growth rate found agree well with linear perturbation theory. Nonlinear evolution of the bar is followed. Role of the growing transient spirals in bar formation is discussed.