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What is dark matter?

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Quick answer

Dark matter is an invisible form of matter that doesn't emit or reflect light but makes up about 27% of the universe. We know it exists because its gravity holds galaxies together and bends light, even though we can't see it directly.

Key things to understand

  1. It doesn't interact with light, so it's invisible to telescopes.
  2. We infer it from gravity — galaxies spin too fast to hold together without extra unseen mass.
  3. It outweighs ordinary matter roughly 5 to 1.
  4. Its true nature is still one of the biggest open questions in physics.

People also ask

How do we know dark matter exists?
Galaxies rotate faster than their visible mass allows, and light bends around invisible mass — both point to unseen matter.
What is dark matter made of?
Unknown — it isn't ordinary atoms; leading candidates are as-yet-undiscovered particles.
Is dark matter the same as dark energy?
No — dark matter pulls things together via gravity; dark energy pushes the universe to expand faster.

Part of the guide: Space & Astronomy →