Definition of Dark Matter

Dark matter is a form of matter that does not reflect or emit light. Although impossible to detect directly using electromagnetic radiation, its existence is inferred from gravitational effects on visible matter, such as stars. Dark matter accounts for 23% of the total mass-energy of the universe, while ordinary matter accounts for less than 5% (the remainder consists of dark energy). The composition of dark matter is unresolved, but possibilities under consideration include massive compact halo objects (MACHOs) and weakly interacting massive particles (WIMPs).

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