Abstract
It has recently been observed that there are no disc galaxies with masses less than 109M⊙ and this cutoff has not been explained. It is shown here that this minimum mass can be predicted using a model that assumes that 1) inertia is due to Unruh radiation, and 2) this radiation is subject to a Hubble-scale Casimir effect. The model predicts that as the acceleration of an object decreases, its inertial mass eventually decreases even faster stabilising the acceleration at a minimum value, which is close to the observed cosmic acceleration. When applied to rotating disc galaxies the same model predicts that they have a minimum rotational acceleration, i.e.: a minimum apparent mass of 1.1×109M⊙, close to the observed minimum mass. The Hubble mass can also be predicted. It is suggested that assumption 1 above could be tested using a cyclotron to accelerate particles until the Unruh radiation they see is short enough to be supplemented by manmade radiation. The increase in inertia may be detectable.