  We introduce two simple online activities to explore the physics of neutron
stars. These provide an introduction to the basic properties of compact
objects, like their masses and radii, for secondary school students. The first
activity explores the idea of the minimum mass of a neutron star. It is
directly linked to the concept of binding energy and follows on from our
previous activities. The second activity focuses on the maximum mass of neutron
stars using a solvable model of the neutron star interior. The activities are
based on spreadsheets, provided as Supplementary Material, and can be easily
adapted to different levels, age groups and discussion topics. In particular,
these activities can naturally lead towards discussions on extrapolations and
limits of theoretical models.
