Unsolved astrophysics problems

The dwarf galaxy problem

Also known as the missing satellites problem

Arises from a mismatch between observed dwarf galaxy numbers and collisionless numerical cosmological simulations that predict the evolution of the distribution of matter in the universe.In simulations

Dark matter clusters hierarchically

In ever increasing numbers of halo blobs as halos' components' sizes become smaller-and-smaller.However

Although there seem to be enough observed normal-sized galaxies to match the simulated distribution of dark matter halos of comparable mass

The number of observed dwarf galaxies is orders of magnitude lower than expected from such simulation.