MULTIFRACTAL PROCESSES AND SELF-ORGANIZED CRITICALITY IN THE LARGE-SCALE STRUCTURE OF THE UNIVERSE

In the past five to ten years mounting evidence has arisen indicating that the large-scale spatial number density of galaxies may be governe d by fractal or multifractal statistics. In this paper we extend this idea by searching for multifractal behaviour in other density fields. Namely, generalized luminosity density fields (which we define here) c onstructed from information on both the angular position and the appar ent luminosity of galaxies. Using data from the Center for Astrophysic s' CfA2 catalogue, we perform various multifractal analyses that revea l that over broad angular scales, the fields studied present two impor tant signatures of multifractal behavior: multiscaling and algebraic p robability distributions associated with extreme fluctuations and firs t-order multifractal phase transitions. Since the presence of both of these phenomena is the defining feature of Self-Organized Criticality, we argue that the spatio-luminous distribution of galaxies in the obs ervable universe may be described as a nonclassical self-organized cri tical phenomenon resulting from multifractal cascades.