Περίληψη :
Massive OB-type stars are predominantly born in stellar associations or clusters. Their copious UV radiation fields, dense stellar winds, and violent supernovae play a dominant role in the momentum and energy budget of the Galaxy. It turns out that, in the first few million years of a cluster’s life, several OB stars are dynamically ejected from the cluster at high speed. At later times, OB runaway stars may also be produced in binaries when the companion explodes as a supernova. The efficiency of both mechanisms is poorly constrained; a hybrid scenario is also possible. I will report on recent astrometric observations obtained with the ESA /Gaia /satellite of some young massive clusters. These observations demonstrate that not just some, but a large fraction of the most massive stars initially born in clusters become runaways. Apparently, model predictions have significantly underestimated the dynamical escape fraction of massive stars. This has important consequences for the determination of the high-mass end of the (initial) stellar mass function, a fundamental aspect of the outcome of the star-formation process. Also, as these runaways may travel hundreds of parsecs such that their supernovae occur far from their place of origin, their role in shaping and heating the interstellar medium and driving galactic outflows is far more important than previously thought.
