Cold refers to the fact that the dark matter moves slowly compared to the speed of light, giving it a vanishing equation of state.
Proposed candidates for CDM include weakly interacting massive particles, primordial black holes, and axions.
[3] A review article in 1984 by Blumenthal, Sandra Moore Faber, Primack, and Martin Rees developed the details of the theory.
Since the late 1980s or 1990s, most cosmologists favor the cold dark matter theory (specifically the modern Lambda-CDM model) as a description of how the universe went from a smooth initial state at early times (as shown by the cosmic microwave background radiation) to the lumpy distribution of galaxies and their clusters we see today—the large-scale structure of the universe.
Dwarf galaxies are crucial to this theory, having been created by small-scale density fluctuations in the early universe;[5] they have now become natural building blocks that form larger structures.
The candidates fall roughly into three categories: Several discrepancies between the predictions of cold dark matter in the ΛCDM model and observations of galaxies and their clustering have arisen.
[19] In this framework, NGC 3109 is too massive and distant from the Local Group for it to have been flung out in a three-body interaction involving the Milky Way or Andromeda Galaxy.