Stars evolve while keeping themselves in hydrostatic equilibrium: this condition corresponds to an almost perfect balance between pressure and gravity forces and renders a shapeless gaseous mass into a nearly spherical nuclear reactor. In fact, in their innermost layers the very hot temperatures allow for thermonuclear reactions heating the gaseous envelope, and counterbalancing its gravity pull. Massive stars can burn elements from Hydrogen up to Iron-Nickel, where the binding energy per nucleon reaches its maximum value: this prevents further burning steps in stellar environments to take place. At this point, gravity gradually overwhelms pressure forces and the matter accreting onto a central skeleton (a proto neutron star) triggers the onset of its gravitational collapse and, eventually, a spectacular explosion known as core collapse supernova, which wipes away the outer gaseous envelope and leaves behind it a neutron star or a black hole.

Stars are often found in binary systems in which they orbit each other in a common gravitational potential well. In turn, neutron stars may be found in binary systems and spiral until their coalescence: a neutron star merger radiates energy away via gravitational waves and decompresses the compact neutron star matter. This phenomenon may provide the necessary physical conditions allowing for the rapid neutron capture process (or simply r-process) nucleosynthesis, i. e. one of the possible mechanisms able to synthesize elements heavier than iron. The nuclear decay of these very heavy elements power a rapidly-evolving, multi-band transient dubbed kilonova (or sometimes macronova). As we are nowadays able to observe gravitational waves with dedicated Ligo/VIRGO interferometers, is it possible to conjugate the electromagnetic (ultraviolet/optical/infrared) observations with the gravitational one in order to more precisely constrain the physics of neutron star mergers, as well as nuclear mass models.Stars are often found in double systems in which they orbit each other in a common gravitational potential well. In turn, neutron stars may be found in binary systems and spiral until their coalescence: such a neutron star merger lose energy via gravitational waves and decompress the compact neutron star matter. This phenomenon may provide the necessary physical conditions allowing for the rapid neutron capture process (or simply r-process) nucleosynthesis, i. e. one of the possible mechanisms able to synthesize elements heavier than iron. The nuclear decay of these very heavy elements power a rapidly-evolving, multi-band transient referred to as kilonova. As we are nowadays able to observe gravitational waves with dedicated Ligo/VIRGO interferometers, is it possible to conjugate the electromagnetic (ultraviolet/optical/infrared) observations with the gravitational one in order to more precisely constrain the physics of neutron star mergers, as well as nuclear mass models.