  We present an analysis of 20 galaxy clusters observed with the Chandra X-ray
satellite, focussing on the temperature structure of the intracluster medium
and the cooling time of the gas. Our sample is drawn from a flux-limited
catalogue but excludes the Fornax, Coma and Centaurus clusters, owing to their
large angular size compared to the Chandra field-of-view. We describe a
quantitative measure of the impact of central cooling, and find that the sample
comprises 9 clusters possessing cool cores and 11 without. The properties of
these two types differ markedly, but there is a high degree of uniformity
amongst the cool core clusters, which obey a nearly universal radial scaling in
temperature of the form T \propto r^~0.4, within the core. This uniformity
persists in the gas cooling time, which varies more strongly with radius in
cool core clusters (t_cool \propto r^~1.3), reaching t_cool <1Gyr in all cases,
although surprisingly low central cooling times (<5Gyr) are found in many of
the non-cool core systems. The scatter between the cooling time profiles of all
the clusters is found to be remarkably small, implying a universal form for the
cooling time of gas at a given physical radius in virialized systems, in
agreement with recent previous work. Our results favour cluster merging as the
primary factor in preventing the formation of cool cores.
