Quantitative determination of minimum spanning tree structures: using the pulsar tree for analysing the appearance of new classes of pulsars

Abstract

In this work, we introduce a quantitative methodology to define what is the main trunk and what are the significant branches of a minimum spanning tree (MST). We apply it to the pulsar tree, i.e. the MST of the pulsar population constructed upon a Euclidean distance over the pulsar’s intrinsic properties. Our method makes use of the betweenness centrality estimator, as well as of non-parametric tests to establish the distinct character of the defined branches. Armed with these concepts, we study how the pulsar population has evolved throughout history and analyse how to judge whether a new class of pulsars appears in new data, future surveys, or new incarnations of pulsar catalogs.