Astronomers are great at this. Three postulated categories of dark matter include: * WIMPs: weakly interacting massive particles * MACHOs: massive compact hal

Astronomers are great at this. Three postulated categories of dark matter include: * WIMPs: weakly interacting massive particles * MACHOs: massive compact halo objects * RAMBOs: robust associations of massive baryonic objects There's also the HERO (hyper extremely red object), which isn't quite dark, but close.