Tracing Competing Paradigms - Mapping Scientific Frontiers: The Quest for Knowledge Visualization - page 218

Fig. 6.12 Supermassive black holes search between 1991 and 1995. The visualization of the
document co-citation network is based on co-citation data from 1981 through 2000. Three
paradigmatic clusters highlight new evidence (the cluster near to the front) as well as theoretical
origins of the AGN paradigm
in the central area. Once these highly cited articles arrive, they will predominant the
overall citation profile of the entire co-citation network (See Fig. 6.12 ).
Citations in the central area remain very quiet, partly because some of the
documents located there were either newly published or not published yet. However,
the visualization of the third period, 1996-2000, clearly shows dramatic drops of the
overall citation profiles of once citation-prosperous clusters in the peripheral areas.
Two of the three distinct clusters have hardly been cited. In contrast, citations at the
center of the network now become predominant (See Fig. 6.13 ). Pathfinder-based
citation and co-citation visualizations are able to outline the movement of the AGN
paradigm in terms of which articles researchers cite during a particular period of
time.
The AGN paradigm is prevailing, but conclusive evidence is still missing. Some
astronomers have suggested alternative explanations. For example, could the mass
concentration in M87 be due to a cluster of a billion or so dim stars such as neutron
stars or white dwarfs, instead of supermassive black holes? Opponents of the AGN
paradigm such as Terlevich and colleagues have made strong arguments in their
articles. Some of these articles are located in a remote area towards the far end of
the co-citation network. In order to study how alternative theories had competed