Dark matter is a form of matter that does not interact with light, meaning it does not emit, absorb, or reflect it, making it invisible and detectable only through its gravitational effects. It is a crucial component of the universe, accounting for approximately 27% of its total mass and energy. It is essential for explaining the observed structure and dynamics of galaxies and the large-scale structure of the cosmos. While its exact nature remains elusive, ongoing research aims to uncover its properties and confirm its existence through various detection methods and theoretical studies.

1. 1. Discovery and Evidence

• • • Galaxy Rotation Curves: Observations of the rotational speeds of galaxies reveal that they rotate much faster than would be expected if only visible matter were present. The discrepancy suggests the presence of unseen mass, which is attributed to dark matter.
    • Gravitational Lensing: Dark matter can bend light from distant objects due to its gravitational influence, a phenomenon known as gravitational lensing. This effect allows astronomers to map the distribution of dark matter in galaxy clusters.
    • Cosmic Microwave Background (CMB): The CMB provides a snapshot of the universe shortly after the Big Bang. Analysing the CMB’s temperature fluctuations helps scientists infer the presence and distribution of dark matter.

 

1. 2. Characteristics

• • • Non-Luminous: Dark matter does not emit or interact with electromagnetic radiation, making it invisible to telescopes that detect light.
    • Massive: It has mass and contributes to the gravitational pull in galaxies and galaxy clusters.
    • Non-Interacting: Dark matter interacts very weakly with ordinary matter, except through gravity. It does not participate in the electromagnetic or strong nuclear forces.

 

1. 3. Types of Dark Matter

• • • Weakly Interacting Massive Particles (WIMPs): One of the leading candidates for dark matter, WIMPs are heavy particles predicted by certain theories beyond the Standard Model of particle physics. They interact through the weak nuclear force and gravity.
    • Axions: Hypothetical lightweight particles that could make up dark matter. Axions are predicted by some extensions of the Standard Model, such as theories involving strong CP violation.
    • Sterile Neutrinos: A type of neutrino that does not interact via the weak nuclear force, unlike regular neutrinos. They are another candidate for dark matter.

 

1. 4. Cosmological Impact

• • • Galaxy Formation and Structure: Dark matter plays a crucial role in the formation and structure of galaxies and galaxy clusters by providing the gravitational framework for visible matter to coalesce and form structures.
    • Large-Scale Structure: It influences the distribution of galaxies and the overall large-scale structure of the universe, shaping the cosmic web of interconnected clusters and filaments.

 

1. 5. Detection Efforts

• • • Direct Detection: Experiments aim to detect dark matter particles directly by looking for rare interactions between dark matter and ordinary matter. Examples include the LUX-ZEPLIN (LZ) experiment and the XENONnT detector.
    • Indirect Detection: Researchers look for signals from the annihilation or decay of dark matter particles, such as high-energy photons or neutrinos, in cosmic rays.
    • Collider Experiments: High-energy particle accelerators, such as the Large Hadron Collider (LHC), seek to create dark matter particles in collisions and study their properties.