All galaxies (including our own) are thought to exist inside a giant cosmological structure called a dark matter halo — a cloud-like phenomenon made up of invisible matter that forms a scaffold to the visible universe.
These halos are key to the formation of stars, which are created as gas is pulled into the halos. Cool temperatures cause the gas to clump together. Over time, some of these clumps grow in size until gravity causes them to collapse, creating friction, which in turn creates heat and (eventually) results in the birth of a protostar.
It is not known whether any dark halos are totally devoid of stars. However, new research published in The Astrophysical Journal Letters suggests that there is a mass below which halos would be unable to make stars — and it is much lower than previously thought.
