Dark matter is a theoretical form of matter that is believed to exist in the universe. It is called "dark" because it does not interact with light or other electromagnetic radiation, making it invisible and difficult to detect using traditional astronomical methods. Its presence is inferred through its gravitational effects on visible matter and the structure of the universe.
Dark matter is different from the ordinary matter we are familiar with, such as atoms and molecules. Unlike normal matter, which consists of particles like protons, neutrons, and electrons, dark matter is hypothesized to be made up of exotic particles that do not interact strongly with electromagnetic forces.
The nature and exact composition of dark matter remain unknown. Various theoretical models suggest different types of particles that could make up dark matter, such as weakly interacting massive particles (WIMPs), axions, or sterile neutrinos. These particles are postulated to have mass and interact primarily through gravity and weak nuclear forces, which are responsible for some types of radioactive decay.
The presence of dark matter is inferred from its gravitational effects on visible matter, such as galaxies, galaxy clusters, and the large-scale structure of the universe. Observations of the rotational speeds of galaxies, gravitational lensing, and the distribution of matter in the universe indicate that there is more mass present than can be accounted for by visible matter alone. Dark matter is thought to play a crucial role in holding galaxies and galaxy clusters together, providing the gravitational glue that prevents them from flying apart based on the observed amount of visible matter.
While dark matter has not yet been directly detected in a laboratory setting, ongoing research and experiments aim to shed light on its true nature and properties. Detecting and understanding dark matter is one of the most significant challenges in modern astrophysics and particle physics.