Galactoseismology: Discovery of vertical waves in the galactic disk

Lawrence M. Widrow, Susan Gardner, Brian Yanny, Scott Dodelson, Hsin Yu Chen

Research output: Contribution to journalArticlepeer-review

219 Scopus citations


We present evidence for a Galactic North-South asymmetry in the number density and bulk velocity of solar neighborhood stars. The number density profile, which is derived from main-sequence stars in the Sloan Digital Sky Survey, shows a (North-South)/(North+South) deficit at |z| ≃ 400 pc and an excess at |z| 800 pc. The bulk velocity profile, which is derived from the Sloan Extension for Galactic Understanding and Exploration, shows a gradual trend across the Galactic midplane as well as smaller-scale features. We speculate that the North-South asymmetry, which has the appearance of a wavelike perturbation, is intrinsic to the disk. We explore the physics of this phenomenon through an analysis of the linearized Boltzmann and Poisson equations and through one-dimensional simulations. The perturbation may be excited by the passage of a satellite galaxy or dark matter subhalo through the Galactic disk, in which case we are witnessing a recent disk-heating event.

Original languageEnglish
Article numberL41
JournalAstrophysical Journal Letters
Issue number2
StatePublished - May 10 2012


  • Galaxy: kinematics and dynamics
  • solar neighborhood

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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