Massive star formation outside → OB associations.
Recent observational findings suggest that → massive star
formation is a collective process. In other words, massive stars form in
→ cluster environments
and the mass of the most massive star in a cluster is correlated with the mass of the
cluster itself. Nevertheless, other observational results give grounds for supposing that
massive stars do not necessarily form in clusters but that they can be formed
as isolated stars or in very small groups. According to statistical studies
nearly 95% of Galactic → O star
population is located in clusters or OB associations.
This means that a small percentage, about 5%, of high mass stars may
form in isolation. Isolation is meant not traceable to an origin
in an OB association. This definition therefore excludes
→ runaway massive stars,
which are thought to result from either dynamical interaction in massive dense clusters,
or via a kick from a → supernova explosion in a
→ binary system. Alternatively, isolated massive star has been
defined as follows: An O-type star belonging to a cluster whose total mass is
< 100 Msun and moreover is devoid of → B stars
(Selier et al. 2011, A&A 529, A40 and references therein).
See also: → isolated; → massive star;
→ formation.
