Baryonic acoustic oscillation
Baryonic acoustic oscillations ( English Baryonic Acoustic Oscillation, BAO ) are density waves , which in the early universe by the interplay of gravity and radiation pressure trained. Their effects can be observed today in the anisotropy spectrum of cosmic background radiation and in the distribution of galaxies . Their precise measurement plays an important role in modern cosmology .
Details
According to popular theory, matter consists of baryonic and dark matter . After the inflation the matter is not distributed absolutely homogeneously , there are initial fluctuations . The baryonic matter is drawn into areas with a higher density of dark matter by gravity , the density of the baryons increases. This increases the photon pressure, pushes the baryonic matter apart again and thus causes the baryon density to decrease. Through this interplay of attraction due to gravity and repulsion due to photon pressure, the baryonic matter begins to oscillate .
This mechanism collapses when radiation and matter are decoupled approx. 380,000 years after the Big Bang . The baryonic matter is now only subject to gravity, but the photons "store" the information about the density of the baryons at their place of origin at the time of decoupling in the form of a temperature .