SUB-GIANT BRANCH EVOLUTION AND EFFICIENT CENTRAL ENERGY-TRANSPORT

We gather and present observational evidence of a problem with the conventional understanding of the late main-sequence and sub-giant branch evolution of globular cluster stars. The difficulties with these supposedly ''well-understood'' phases of stellar evolution manifest themselves in both sub-giant and red-giant branch anomolies (relative to main-sequence normalization) in recent, accurate, CCD-derived luminosity functions. Attempts to reproduce these features using conventional theory and fairly conventional modifications have failed. However, we show that the anomalies, now known to exist in four classical metal-weak clusters including the historical archetype M92 and the now even more thoroughly surveyed M30, are consistent with simple predicted consequences of highly efficient central energy transport inside such stars. If these results and our interpretation survive, then globular clusters may be younger than usually thought by up to approximately 20%. Although any sufficiently effective energy transport mechanism would help explain the observations, one intriguing possibility is transport due to WIMPs (weakly interacting massive particles). In this case, globular clusters may have acted as giant detectors for such particles. These potentially significant results require further investigation with more detailed and specific models and more observational data, which should be relatively easy to obtain on 2 m class telescopes.