The candidates for Dark Matter
Baryonic (e.g. made of protons and neutrons, normal matter):
- Beer cans
- Jupiter size objects (failed stars)
- very low mass stars
- black holes and other stellar remnants
Non-baryonic (exotic matter):
- neutrinos with mass --> because there are so MANY neutrinos
even a tiny neutrino mass has cosmological significance
- WIMPS - weakly interacting massive particles created in the extremely
early universe
- Particles associated with symmetry breaking
Changes in Gravity?
- Maybe we don't understand gravity so well? This excuse is
not favored, but should not be discounted entirely.
How much dark matter is there?
- Theory --> 99% of the Universe is Dark Matter
- Observations --> 90% of the Universe is Dark Matter and the
Universe is open
The above ideas are still hugely debated. But currently, the
evidence indicates:
- Neutrinos are now know to have some mass, though its not sufficient
to explain the missing matter.
- WIMPs have not been ruled out, nor proven, and yet remain a hopeful
source of dark matter.
- MACHOs have been detected in our halo, (stellar remnants, and
low mass stars) may make up as much as 1/4 to 1/2 the dark matter.