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The heating of gas in a galaxy cluster by X-ray cavities and large-scale shock fronts


Most of the baryons in galaxy clusters reside between the galaxies in a hot, tenuous gas1. The densest gas in their centres should cool and accrete onto giant central galaxies at rates of 10–1,000 solar masses per year1. No viable repository for this gas, such as clouds or new stars, has been found1. New X-ray observations, however, have revealed far less cooling below X-ray temperatures than expected2, altering the previously accepted picture of cooling flows. As a result, most of the gas must be heated to and maintained at temperatures above 2 keV (ref. 3). The most promising heating mechanism is powerful radio jets emanating from supermassive black holes in the central galaxies of clusters4. Here we report the discovery of giant cavities and shock fronts in a distant (z = 0.22) cluster caused by an interaction between a radio source and the hot gas surrounding it. The energy involved is 6 × 1061 erg, the most powerful radio outburst known. This is enough energy to quench a cooling flow for several Gyr, and to provide 1/3 keV per particle of heat to the surrounding cluster.

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Figure 1: The relationships between the X-ray, radio and optical emissions of the cluster.
Figure 2: Projected temperature and pressure profiles of the cluster gas.
Figure 3: Projected 0.5–7.5-keV radial surface brightness profile of the cocoon region compared to shock-model predictions.
Figure 4: Temperature map of the central 200 × 200 arcsec of the cluster.


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B.R.McN. thanks G. Evrard, D. De Young, M. Sharma and J. Shields for discussions. The National Radio Astronomy Observatory is operated by Associated Universities Inc., under cooperative agreement with the National Science Foundation. This work was supported by a NASA Long Term Space Astrophysics grant, a Chandra Archival Research grant, a Chandra Guest Observer grant, and a contract from the Department of Energy through the Los Alamos National Laboratory.

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McNamara, B., Nulsen, P., Wise, M. et al. The heating of gas in a galaxy cluster by X-ray cavities and large-scale shock fronts. Nature 433, 45–47 (2005).

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