The strongest fundamental force of nature generates ~96% of the mass of the visible universe and binds together the building blocks of quantum chromodynamics, quarks and gluons, within the proton. At temperatures of a few trillion Kelvin these quarks and gluons strongly interact in an exotic state of matter known as the quark-gluon plasma, which behaves as a nearly perfect liquid. Collider experiments have been smashing heavy-ions together at nearly the speed of light in order to produce tiny droplets of the quark-gluon plasma in the laboratory with a size of the order of trillionth cm. Neutron star mergers may reach a similar state of deconfined quarks but at large densities and vanishing temperatures and on much larger scales. Using both heavy-ion collisions and neutron stars mergers, one can begin to understand the phase diagram of quantum chromodynamics and in particular search for interesting features such as a critical point or first-order phase transition separating quarks and gluons from hadrons. In this talk I will discuss recent progress made in understanding the quantum chromodynamics phase diagram, leveraging the synergies between heavy-ion collisions and neutron star mergers.