Galaxies appear simpler than expected

摘要

Galaxies are complex systems the evolution of which apparently results fromthe interplay of dynamics, star formation, chemical enrichment, and feedbackfrom supernova explosions and supermassive black holes. The hierarchical theoryof galaxy formation holds that galaxies are assembled from smaller pieces,through numerous mergers of cold dark matter. The properties of an individualgalaxy should be controlled by six independent parameters including mass,angular-momentum, baryon-fraction, age and size, as well as by the accidents ofits recent haphazard merger history. Here we report that a sample of galaxiesthat were first detected through their neutral hydrogen radio-frequencyemission, and are thus free of optical selection effects, shows fiveindependent correlations among six independent observables, despite having awide range of properties. This implies that the structure of these galaxiesmust be controlled by a single parameter, although we cannot identify thisparameter from our dataset. Such a degree of organisation appears to be at oddswith hierarchical galaxy formation, a central tenet of the cold dark matterparadigm in cosmology.