Baryon Acoustic Oscillations
First published: 2009
Brief summary
Review of BAO as relic sound-wave imprints in the early universe and a standard ruler for cosmology.
Article
Baryon acoustic oscillations are the remaining imprint of sound waves that travelled through the hot plasma of the early universe before atoms formed. Gravity drew matter into overdense regions, while radiation pressure opposed compression, producing propagating acoustic disturbances in the coupled photon–baryon fluid.
When the universe cooled sufficiently for electrons and nuclei to combine, photons decoupled from ordinary matter and the acoustic propagation effectively stopped. The maximum distance travelled by the sound waves established a characteristic comoving scale that was preserved in the later distribution of galaxies and matter.
Astronomers detect this scale statistically as a small excess in the probability of finding pairs of galaxies separated by a particular distance. The same physical scale is also related to the acoustic structure observed in the cosmic microwave background.
Because the characteristic scale can be calculated from early-universe physics, it serves as a standard ruler. Measurements across different redshifts constrain the expansion history, spatial geometry and properties of dark energy, while requiring careful treatment of survey selection, nonlinear evolution and statistical uncertainty.
Source details and credits
- Source / publisher: arXiv
- Source type: Review
- URL type: WWW
- Credits: arXiv
- URL: https://arxiv.org/abs/0910.5224