Hidden Growth of Supermassive Black Holes in Galaxy Mergers

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Science  30 Apr 2010:
Vol. 328, Issue 5978, pp. 576-578
DOI: 10.1126/science.1189695

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Black holes are found at the centers of massive galaxies. Although no light escapes from them, their presence can be revealed by the glow of surrounding gases compressed and heated by the driving force of the black hole's gravitation. This quasar emission ranges from low-energy radio waves to the highest-energy gamma-ray region of the electromagnetic spectrum. Quasar formation can be driven by galaxy mergers, which change the distribution of gas around the black hole. This process can also create stars that supernova and create interstellar dust that obscures our view of galactic centers in the visible to x-ray regions. On page 600 of this issue, Treister et al. (1) present an analysis of data from several space-based telescopes, showing that a greater fraction of quasars that formed in the early universe were obscured by dust, compared with its later stages. This is consistent with observational evidence on the evolution over cosmic time of gas-rich galaxies and a theoretical model for the rate at which they merge.