Hot dark matter

[3] In terms of its application, the distribution of hot dark matter could also help explain how clusters and superclusters of galaxies formed after the Big Bang.

Because cold dark matter possesses a lower velocity, it could be the source of "smaller, galaxy-sized lumps," as shown in the image.

[4] Hot dark matter, then, should correspond to the formation of larger mass aggregates that surround whole galaxy clusters.

However, data from the cosmic microwave background radiation, as measured by the COBE satellite, is highly uniform, and such high-velocity hot dark matter particles cannot form clumps as small as galaxies beginning from such a smooth initial state, highlighting a discrepancy in what dark matter theory and the actual data are saying.

Theoretically, in order to explain relatively small-scale structures in the observable Universe, it is necessary to invoke cold dark matter or WDM.