Astronomers found the Milky Way lies within a massive flat sheet of dark matter about 32 million light-years across. Simulations show this structure and nearby cosmic voids balance gravitational forces, explaining why most nearby galaxies move away instead of falling toward the Local Group.​Astronomers found the Milky Way lies within a massive flat sheet of dark matter about 32 million light-years across. Simulations show this structure and nearby cosmic voids balance gravitational forces, explaining why most nearby galaxies move away instead of falling toward the Local Group.  ​ science