Further detailed deep studies with Chandra and XMM-Newton as well as future studies with Constellation-X and Xeus are needed in order to better understand the heating/cooling balance. There is considerable potential for studies of the cool and warm gas and dust around the BCG using HST, Spitzer and ground-based telescopes. Larger cluster samples are needed, particularly at medium to high redshifts. Determining the extent of a heating-cooling balance (or not) in groups, elliptical galaxies, and galaxy bulges is also important as is the evolution of any balance in all massive objects.
We thank Mateusz Ruszkowski, Mitch Begelman, Roger Blandford, and an anonymous referee for a careful reading of this manuscript. ACF thanks the Royal Society for support. JRP was supported by a grant from NASA for scientific and calibration support of the RGS at Stanford. This was also supported by the U.S. Department of Energy under contract number DE-AC02-76SF00515.