From studying the effects of gravity on both matter and light, it has been discovered that the universe contains much more matter than is accounted for by visible objects; stars, galaxies, nebulas and interstellar gas. This unseen matter is known as dark matter, (dark means that there is a wide range of strong indirect evidence that it exists, but we have not yet detected it directly) having come into existence alongside the rest of the physical universe before gradually gathering into a foam -like structure of filaments and voids and allowing other forms of matter to form together into visible structures. The ΛCDM model is the most widely accepted model of the universe. It suggests that about 69.2% ± 1.2% of the mass and energy in the universe is dark energy which is responsible for the acceleration of the expansion of the universe, and about 25.8% ± 1.1% is dark matter. Ordinary (' baryonic ') matter is therefore only 4.84% ± 0.1% of the physical universe. Stars, planets, and visible gas clouds only form about 6% of the ordinary matter.