Hot bubbles from active galactic nuclei as a heat source in cooling-flow clusters


Hot, X-ray-emitting plasma permeates clusters of galaxies. The X-ray surface brightness often shows a peak near the centre of the cluster that is coincident with a drop in the entropy of the gas. This has been taken as evidence for a ‘cooling flow’, where the gas cools by radiating away its energy, and then falls to the centre1. Searches for this cool gas have revealed significantly less than predicted2, indicating that the mass deposition rate is much lower than expected. Most clusters with cooling flows, however, also host an active galactic nucleus at their centres3. These active galactic nuclei can inflate large bubbles of hot plasma that subsequently rise through the cluster ‘atmosphere’, thus stirring the cooling gas4,5 and adding energy. Here we report highly resolved hydrodynamic simulations which show that buoyant bubbles increase the cooling time in the inner regions of clusters and significantly reduce the deposition of cold gas.

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Figure 1: Snapshots of the density at two different times in our simulation (run 2).
Figure 2: Average specific entropy of the ambient material in units of 3.1 × 1027 erg cm2 g-5/3 at different heights.
Figure 3: Cooling time of the ambient material averaged over horizontal slices.


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The computations reported here were performed using the UK Astrophysical Fluids Facility (UKAFF). The software used in this work was in part developed by the DOE supported ASCI/Alliances Center for Thermonuclear Flashes at the University of Chicago.

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Correspondence to Marcus Brüggen.

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Brüggen, M., Kaiser, C. Hot bubbles from active galactic nuclei as a heat source in cooling-flow clusters. Nature 418, 301–303 (2002).

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