OB association

An OB association is a loosely organized, gravitationally unbound group of young, massive, main sequence stars primarily of spectral types O and B, characterized by their high temperatures, blue color, luminous, and massive stars with masses between 10 and 90 times that of the Sun. Sometimes these late O and Early B stars are referred as OB stars. These associations typically contain 10 to 100 (or more) massive stars alongside numerous lower-mass stars, all sharing common motion vectors, ages, and chemical compositions, indicating a shared origin. Unlike denser star clusters, OB associations lack sufficient gravitational binding and can disperse over millions of years.