What is Dark Matter ?

Dark matter is a mysterious substance that makes up approximately 27% of the total mass-energy content of the universe, according to current cosmological models. Despite its name, dark matter does not emit, absorb, or reflect light, making it invisible and detectable only through its gravitational effects on visible matter and light.

Key points about dark matter include:

1. Invisible and Undetectable: Dark matter does not emit, absorb, or reflect electromagnetic radiation, including visible light, X-rays, or radio waves. As a result, it cannot be observed directly using traditional telescopes or instruments.
2. Gravitational Effects: Dark matter interacts with ordinary matter and light primarily through gravity. Its gravitational effects can be observed indirectly, such as through the gravitational lensing of light from distant galaxies or the motion of stars and galaxies within galaxy clusters.
3. Cosmic Structure Formation: Dark matter plays a crucial role in the formation and evolution of cosmic structures, including galaxies, galaxy clusters, and the large-scale structure of the universe. Its gravitational pull helps to bind galaxies together and provides the scaffolding for the formation of cosmic structures.
4. Composition and Nature: The exact nature of dark matter remains unknown. Various theoretical models propose different types of particles as candidates for dark matter, including weakly interacting massive particles (WIMPs), axions, sterile neutrinos, and others. Experimental efforts, such as those conducted in particle accelerators and underground detectors, aim to detect and characterize dark matter particles directly.
5. Dark Energy: Dark matter should not be confused with dark energy, another mysterious component of the universe that constitutes approximately 68% of its total mass-energy content. Dark energy is thought to be responsible for the observed accelerated expansion of the universe, while dark matter primarily influences the formation and distribution of cosmic structures.

Despite decades of research, the true nature of dark matter remains one of the most significant unsolved mysteries in modern physics and cosmology. Its existence is inferred from its gravitational effects on the universe, but detecting and understanding dark matter particles directly remain major challenges for scientists.