Red, but Not Dead

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Science  04 Oct 2002:
Vol. 298, Issue 5591, pp. 17
DOI: 10.1126/science.298.5591.17b

Rich clusters contain thousands of galaxies. In the process of forming these clusters, the gas from the galaxies is stripped away and concentrated in the cluster center, where it cools quickly and is a major, but short-lived, source of fuel for star formation and for supermassive black holes. Red clusters were thought to be relatively old and quiescent systems in which the gas has been consumed and star formation and supermassive black holes are rare.

Martini et al. have found six supermassive black holes in the supposedly quiet red cluster Abell 2104. They identified the characteristic energetic x-ray radiation of actively accreting black holes using the Chandra X-ray Observatory and then confirmed that these black holes were indeed members of the cluster, using the 6.5-m Walter Baade optical telescope. This unexpected overabundance of black holes indicates that the galaxies have somehow held onto their endowment of gas, which is being used to nourish these sprightly black holes. These results have intriguing implications for galaxy evolution and for the care and feeding of black holes in clusters. — LR

Astrophys. J.576, L109 (2002).

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