OB stars are very hot blue stars with thick atmospheres. (astro-canada.ca)
B stars have similar properties to O stars (that is, they are very hot blue stars with thick atmospheres) but have lower surface temperatures. (astro-canada.ca)
But because the journey took 100 million years, and hot blue stars only live about a third that long, the star should have gone kaput long ago. (sciencemag.org)