While physics laws are the same in the laboratory as in the cosmos, the physical conditions are most often very different. We meet in astrophysics conditions that cannot be reproduced in the laboratory. This is for example true of density, where we find in the cores of neutron stars densities as high as 1015 g cm − 3, ten times the density of nuclei, while the density of extragalactic space is less than 10 − 29 g cm − 3. Both extremes cannot be generated in the laboratory. It is therefore worth setting the scene by listing those objects that will form the core of our interest and by looking at the parameter space in which most of our study will focus.