Intergalactic voids are changing size and merging

Nature : Cosmic voids are large volumes of empty space between galaxy clusters. Reaching sizes of 50 Mpc, the voids have so little material in them that it was thought that they would just be pushed and pulled along by the movements of the rest of the universe. However, a comparison of simulations and data collected by the Sloan Digital Sky Survey (SDSS) revealed that many of the voids are moving faster than they would if they were being carried by the movements of surrounding material. Diego Lambas of the National University of Cordoba in Argentina and his colleagues also found that smaller voids were getting squished together and that larger voids were growing in size. Their observations of the SDSS data revealed that the smaller voids are located in areas of the cosmic web with higher-than-average densities, and as a result, gravity in those regions is forcing the voids to collapse. The reverse is true for the larger voids.