What is dark matter made of?
In plain words
Galaxies, clusters and the cosmic microwave background all require extra unseen mass, about five times the ordinary matter. The task is to find out what that mass physically is.
Precise statement
Determine the microscopic identity (mass, spin, non-gravitational couplings, production mechanism) of the non-baryonic component with $\Omega_c h^{2} = 0.120 \pm 0.001$ inferred from the CMB in LCDM. An answer is a candidate confirmed by a reproducible non-gravitational signal (direct, indirect or collider detection, or a compact-object census) whose abundance accounts for $\Omega_c$.
What would settle it
A reproducible non-gravitational detection of a candidate whose inferred cosmic abundance matches $\Omega_{c}$.
Status in the literature
Unverified note
No candidate has been detected as of 2026; the leading searches (xenon detectors, axion haloscopes, gamma-ray telescopes, microlensing) report null or contested results.
Related problems
- More general than Scalar ultralight dark matter coupled to photons: detect or exclude
- More general than Is dark matter the QCD axion?
- More general than Is dark matter self-interacting with a velocity-dependent cross section?
- More general than Is dark matter a thermal-relic weakly interacting massive particle?
- More general than Can asteroid-mass primordial black holes be all the dark matter?