Mon. Not. R. Astron. Soc. 452, 1052–1059 (2015)

Matter, as well as dark matter, is not uniformly distributed throughout the Universe. There are clumps, filaments and voids, for example, the Local Void — a vast emptiness — near our own Local Group of galaxies that includes the Milky Way, Andromeda and many dwarf galaxies. To better understand the structure and dynamics of galaxies, Noam Libeskind and co-workers use the Cosmicflows-2 survey of peculiar velocities to map the movement of local galaxies out to 150 parsecs. They find a filament of dark matter bridging the Local Group and the massive Virgo cluster roughly 50 million light years away. It is simultaneously being stretched by the Virgo cluster and squeezed by the Local Void plus smaller voids from the sides.

This dark matter 'superhighway' channels dwarf galaxies between galaxy clusters. Other studies have revealed that dwarf galaxies are often compressed into planes that are possibly co-rotating. The authors show that four out of the five vast planes of dwarf galaxies are aligned with the main direction of compression (and the direction of expansion of the Local Void). This connection between large-and small-scale structures will help refine models, such as the prevailing cold dark matter model.