Blue supergiant

They are most often an evolutionary phase between high-mass, hydrogen-fusing main-sequence stars and helium-fusing red supergiants,[4][5][6] although new research suggests they could be the result of stellar mergers.

The dividing line is approximately 40 M☉, although the coolest and largest red supergiants develop from stars with initial masses of 15–25 M☉.

It is not clear whether more massive blue supergiants can lose enough mass to evolve safely into old age as a Wolf Rayet star and finally a white dwarf, or they reach the Wolf Rayet stage and explode as supernovae, or they explode as supernovae while blue supergiants.

[18] Now it is known from observation that almost any class of evolved high-mass star, including blue and yellow supergiants, can explode as a supernova although theory still struggles to explain how in detail.

Despite their rarity and their short lives they are heavily represented among the stars visible to the naked eye; their immense brightness is more than enough to compensate for their scarcity.

[citation needed] Blue supergiants have fast stellar winds and the most luminous, called hypergiants, have spectra dominated by emission lines that indicate strong continuum driven mass loss.

Blue supergiants show varying quantities of heavy elements in their spectra, depending on their age and the efficiency with which the products of nucleosynthesis in the core are convected up to the surface.

In some cases, several concentric faint shells can be seen from successive episodes of mass loss, either previous blue loops from the red supergiant stage, or eruptions such as LBV outbursts.