Abstract

I will review the main properties of young superstar clusters (SSCs) and then show that there are two different stationary hydrodynamic solutions for the matter re-inserted by the plethora of massive stars that, as they evolve, undergo strong winds and eventually explode as supernovae. One of the solutions is a full stationary wind. This has a strong impact on the interstellar medium. I will show that the structure of Giant HII regions and HII galaxies is caused by a dramatic competition between the two negative feedback events: the mechanical energy and the UV ionizing radiation arising from SSCs.

The second hydrodynamical solution, now called the bimodal solution, is unavoidable for the more dense and compact clusters. In these cases, the cluster wind is much smaller than what it has been predicted by synthesis models. The fact is that the densest central regions become strongly radiative, what depletes rapidly their pressure, making them unable to reach the required speeds to participate in a wind. In these cases the re-inserted matter accumulates within the cluster volume, causing a positive star formation feedback, as gravity overcomes this matter