Atoms or the ordinary matter constitutes the smallest proportion in the composition of universe, which is only about 4.6%. This includes planets, stars, galaxies, and interstellar gas. The visible component accounts for less than 10% of the ordinary matter, and most of the remaining matter is not seen. The matter in this category, can be like the Sun which emits light and also like the moon which reflects the light. Stars, because of their massive sizes are often considered as a major constituent of ordinary matter, but all stars together account for only 0.5% of the total mass of the universe.
Dark matter constitutes 23% of the total energy in the universe. The substantial mass of galaxies, which cannot be seen unlike stars, planets, and various gases, can only be felt due to its interaction with atoms and radiation through gravity. Unlike ordinary matter, it does not absorb or reflect light but only exerts a gravitational pull. The nature of dark matter is assessed in various forms including Brown Dwarfs and supermassive black holes.
Brown Dwarf is a star whose mass is less than one twentieth of the Sun because of which its core does not burn as a luminous object. Such stars can only shine due to their gravitational contraction. Likewise, black holes are believed to be large in number forming the dark matter as these holes have such an intense gravitational field that no radiation or matter can escape from it.
72% of the energy is spread uniformly across the universe in the form of dark energy, which is responsible to accelerate the expansion of the universe. This form of energy possesses a repulsive force due to anti-gravitational properties. It is because of this repulsive force that is causing the universe to expand faster. Properties of space discovered by Einstein provide explanation to the expansion of universe by dark energy present in the universe. One of the properties states that â€œempty spaceâ€ can possess its own energy. This energy would continue to remain and would not disappear even if universe expands because it is a property of space. Since this energy would increase with time, as more space would come into existence, it would pull the galaxies apart. The diagram shows the changes in the rate of expansion of the universe over time.