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In the 1970s, Professors James Peebles and Jeremiah Ostriker's computer model simulations of galaxies suggested that there are large amounts of unaccounted for matter in the Universe. However, their ideas did not gain wider acceptance until Vera Rubin's measurements of the speeds of stars in galaxies also suggested that there is missing matter, which is now known as dark matter.

["The size and mass of galaxies and the mass of the universe" copyright Ostriker and Peebles-The Astrophysical Journal 193 / "Dark Matter and the origin of galaxies and globular star clusters" copyright Peebles - The Astrophysical Journal 277: 470-477]