According to the standard model of cosmology, the vast majority of galaxies are surrounded by a halo of dark matter particles.

This halo is invisible, but its mass exerts a strong gravitational pull-on galaxy in the vicinity.

A study suggests that the dwarf galaxies of Earth's second closest galaxy cluster known as the Fornax Cluster are free of such dark matter halos.

Dwarf galaxies are small, faint galaxies that can be found in galaxy clusters. Because of this, they might be affected by the gravitational effects of their larger companions.

Tides arise when gravity from one body pulls differently on different parts of another body. These are similar to tides on Earth, because the moon pulls more strongly on the side of Earth.

The Fornax Cluster has a rich population of dwarf galaxies. Observations show that some of these dwarfs appear distorted, as if they have been perturbed by the cluster environment.

The expected level of disturbance of the dwarfs, which depends on their internal properties and their distance to the gravitationally powerful cluster centre.

Galaxies with large sizes but low stellar masses and galaxies close to the cluster centre are more easily disturbed or destroyed.

The authors concluded that, in the standard model, it is not possible to explain the observed morphologies of the Fornax dwarfs in a self-consistent way.

They compared the results with their observed level of disturbance evident from photographs taken by the VLT Survey Telescope of the European Southern Observatory.