Scientists think that they may have an answer for why their simulations show merging pairs of supermassive black holes sometimes result in one of the black holes being suddenly "kicked" away. Though such kicking hasn't been observed, astronomers have some evidence for huge rogue black holes that may have been ejected from centers of galaxies during one of these kicks. The answer, it seems, might come from the interaction of "tendex" and "vortex" lines.
The trouble is that mapping the warping effects of gravity over space-time is incredibly difficult. Each point on such a map has 10 numbers associated with it, making it difficult to analyze. Instead of numbers, the Cornell team lead by Robert Owen used arrows which they then connected into larger lines, similar to the mapping of magnetic fields. These can be generally organized into two types of lines: "tendex," which show the stretching/compressing force of gravity, and "vortex" which describes twisting forces.