We investigated the smoothing of the anisotropy of the cosmic background radiation (CBR) through multiple gravitational scattering. The CBR is gravitationally scattered by galaxies, clusters of galaxies, and superclusters during its travel from the last scattering surface. Although this effect was thought to be unimportant, we found that gravitational scattering by superclusters can reduce the anisotropy of the CBR appreciably. We took into account the fact that the distance between nearby photons increases exponentially through multiple scattering. The angle between the directions of two photons increases due to passage by a scattering object. The change in the relative angle is due to the tidal force, which is proportional to the distance between two photons. As a result, the increase in the relative angle is proportional to the distance between photons. This mechanism leads to an exponential growth of the distance. The exponential growth stops when the distance reaches the mean projected separation between the scattering objects. This exponential growth has been neglected in previous studies. We found that multiple gravitational scattering by superclusters can reduce the observed temperature anisotropy of the CBR by 40--60% from the intrinsic one at a scale of a few degrees, provided that the superclusters were formed at z =~ 2--4.
Publications of the Astronomical Society of Japan
- Pub Date:
- October 1995
- COSMIC BACKGROUND RADIATION;
- GRAVITATIONAL LENSES;
- LARGE-SCALE STRUCTURE OF UNIVERSE