What is dark matter? We don’t know. This is actually one of the most important unanswered questions in modern astronomy. A few ideas: –MACHOS –neutrinos –WIMPS
MACHOs: MAssive Compact Halo Objects Dim, dark objects with masses < 1 M –Brown dwarfs –White dwarfs –Black holes Search for MACHOs used gravitational lensing. Low mass MACHOs (10 -6 -0.1 M ) not significant part of dark matter halo. MACHOs of 0.5 M account for about half of dark matter. –What else is out there?
Other dark matter candidates Neutrinos –If neutrinos are sufficiently massive and enough are present in the galaxy then it is possible they could be the missing dark matter. –Neutrino oscillations require that neutrinos have mass, but it is very small (~10 -10 m electron ). –Neutrinos must be part of dark matter, but it is unclear how much. WIMPs –Weakly Interacting Massive Particles –Predicted by some theories but not yet confirmed experimentally.