Discovery and studies of stellar associations. The Key to Understanding Star Evolution

The review presents works carried out in BAO in the period 1947-70. It tells about the history and significance of one of the greatest discoveries of the twentieth century - stellar associations. Among the fundamental works of Ambartsumian and BAO studies of stellar associations occupy a special place. Their discovery radically changed the existing theories of star formation and evolution and "revived" the slowly dying (as previously assumed) Universe. The discovery of stellar associations proved that star formation occurs in our era. Ambartsumian's ideas clarified the existing and somewhat confusing theory of stellar evolution and gradually became one of the generally accepted directions of the theory of stellar evolution. For more than 75 years, scientists from the BAO and many observatories around the world have been studying stellar associations, but surprises and discoveries are not exhausted. Metaphorically, one can say that for a long time astronomers will follow the path illuminated by stellar associations.