||A star whose mass is larger than approximately 10 solar masses. The spectral types
of massive stars range from about B3 (B star) to O2 (O star) and include Wolf-Rayet
stars as well as Luminous Blue Variables. Massive stars are very rare; for each star
of 20 solar masses there are some 100,000 stars of 1 solar mass. Despite this rarity,
they play a key role in astrophysics. They are major sites of nucleosynthesis beyond
oxygen and, therefore, are mainly responsible for the chemical evolution of galaxies.
Due to their high ultraviolet flux and powerful stellar winds, they bring about interesting
phenomena in the interstellar medium, like H II regions, turbulence, shocks, bubbles,
and so on. Massive stars are progenitors of supernovae (type Ia, type Ic and type
II), neutron stars, and black holes. The formation processes of massive stars is still
an unresolved problem. For massive stars the accretion time scale is larger than the
Kelvin-Helmholtz time scale. This means that massive stars reach the main sequence
while accretion is still going on.