Time-dependent Pattern Speeds in Barred Galaxies

Yu Ting Wu, Daniel Pfenniger, Ronald E. Taam

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


Based on a high-quality N-body simulation of a double-bar galaxy model, we investigate the evolution of the bar properties, including their size, strength, and instantaneous pattern speed derived by using three distinct methods: the Fourier, Jacobi integral, and moment of inertia methods. The interaction of the two bars, which rotate at distinct speeds, primarily affects the size, strength, and pattern speed of the inner bar. When the two bars are perpendicular to each other, the size and the pattern speed of the inner bar decrease and its strength increases. The emergence of a strong Fourier m = 1 mode increases the oscillation amplitude of the size, strength, and pattern speed of the inner bar. On the other hand, the characteristics of the outer bar are substantially influenced by its adjacent spiral structure. When the spiral structure disappears, the size of the outer bar increases and its strength and pattern speed decrease. Consequently, the ratio of the pattern speed of the outer bar with respect to the inner bar is not constant and increases with time. Overall, the double-bar and disk system displays substantial high-frequency semichaotic fluctuations of the pattern strengths and speeds in both space and time, superposed on the slow secular evolution, which invalidates the assumption that the actions of individual stars should be well conserved in barred galaxies, such as the Milky Way.

Original languageEnglish (US)
Article number152
JournalAstrophysical Journal
Issue number2
StatePublished - Jun 20 2018


  • Galaxy: kinematics and dynamics
  • galaxies: evolution
  • galaxies: kinematics and dynamics
  • galaxies: spiral
  • methods: numerical

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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