HADES is a multi-purpose charged-particle detector operated at the SIS18 synchrotron located at the GSI Helmholtz Center for Heavy Ion Research in Darmstadt, Germany. The provided ion beam energies of 1-2 A GeV are among the lowest of all currently running heavy-ion experiments and result in the highest baryo-chemical potentials at freeze-out in case of Au+Au collisions. The HADES heavy-ion program focuses on various observables: (sub-threshold) strangeness production, particle flow and its anisotropies, virtual photon emission and net-proton number fluctuations and is supplemented by more elementary reactions induced by protons and pions.
We compare the modeling of heavy-ion collisions at HADES with neutron star collisions and show that they probe the same part of the phase diagram. We further discuss the different contributions adding up to the finally measured hadron spectra using $K^-$ mesons as an example.