Cosmic Ringing

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Science  18 Nov 2005:
Vol. 310, Issue 5751, pp. 1091
DOI: 10.1126/science.310.5751.1091d

Gravitational attraction causes galaxies to clump together ever more strongly over time, creating a cosmic web of filaments, clusters, and superclusters. Tiny density fluctuations in the hot early universe, including ripples caused by sound waves in the plasma, have been amplified by gravity to produce the galaxy structures we see today. The faint ringing of these sound waves has been picked up in the distribution of the millions of galaxies mapped in the Sloan Digital Sky Survey.

Eisenstein et al. measured the correlation function of luminous red galaxies from the survey, finding a strong signal corresponding to structures with sizes of 100 Mpc, typical of superclusters of galaxies. This scale is as predicted from theories of structure in the cosmic microwave background, linking the physics of sound waves in the early universe to galaxy distributions. Eisenstein et al. use this correspondence to measure the overall density of matter in the universe (30%) and to infer the presence of dark energy. — JB

Astrophys. J. 633, 560 (2005).

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