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Overview
Dark matter is a form of matter that does not emit, absorb, or reflect light in ordinary detectable ways, but it appears to exert gravity. Evidence for dark matter comes from galaxy rotation, galaxy clusters, gravitational lensing, and large-scale cosmic structure.
Evidence
Astronomers infer dark matter from gravitational effects that cannot be explained by visible matter alone.
Galaxy Rotation
Stars far from galactic centers often orbit faster than expected from visible matter, suggesting additional unseen mass.
Gravitational Lensing
Mass bends light. Observed lensing patterns reveal more gravitational mass than visible matter provides in many systems.
Cosmic Structure
Dark matter helps explain how galaxies and galaxy clusters formed and arranged themselves over cosmic time.
Not Dark Energy
Dark matter and dark energy are different ideas. Dark matter clumps gravitationally, while dark energy is associated with accelerated cosmic expansion.
Candidate Particles
Possible dark matter candidates include new particles beyond the standard model, though the exact nature remains unknown.
Common Mistakes
A common mistake is thinking dark matter is ordinary matter hidden in shadows. It is called dark because it does not interact with light in the usual detectable way.
Why This Matters in Physics
Dark matter is central to astrophysics and cosmology because it shapes galaxies, clusters, and the large-scale structure of the universe.