Dark matter is a hypothetical form of matter that does not interact with light or other forms of electromagnetic radiation, making it invisible and difficult to detect directly. Its presence is inferred through its gravitational effects on visible matter and the structure of the universe.
The exact nature of dark matter remains unknown, and its composition is a subject of active scientific research. Several theories and particle candidates have been proposed to explain dark matter, including:
Cold Dark Matter (CDM): This is the most widely accepted theory, suggesting that dark matter consists of non-interacting, slow-moving particles. These particles, often referred to as Weakly Interacting Massive Particles (WIMPs), have yet to be observed directly but are postulated based on their potential gravitational influence.
Axions: Axions are hypothetical particles that are extremely light and would interact weakly with normal matter. They were originally proposed to solve certain problems in particle physics, but they are also considered as potential dark matter candidates.
Modified Gravity Theories: Instead of postulating the existence of new particles, these theories propose modifications to our understanding of gravity. They suggest that our current understanding of gravity may not fully describe the behavior of matter on large scales and that dark matter is an artifact of these modifications.
In terms of its interactions with known particles and forces, dark matter is thought to primarily interact gravitationally. It does not interact via the electromagnetic force, which means it neither emits nor absorbs light. Dark matter does not participate in the strong nuclear force that binds atomic nuclei, and it interacts only weakly with normal matter through the weak nuclear force.
The gravitational effects of dark matter are observed on galactic scales. It helps explain the rotation curves of galaxies, the dynamics of galaxy clusters, and the large-scale structure of the universe. Dark matter's gravitational pull affects the motion of visible matter, providing the necessary gravitational glue for galaxies to form and preventing them from flying apart.
While dark matter's specific nature and interactions are still unknown, ongoing experiments, such as the search for WIMPs and studying the cosmic microwave background radiation, aim to shed light on this elusive component of the universe and deepen our understanding of its role in the cosmos.