A large B star surrounded by the nebula NGC 2023. It lies about 1,600 light-years away. Credit: Adam Block / NOAO /AURA/ NSF.
A B star is a large, luminous, blue-white star of spectral type B with a surface temperature of 10,200 to 30,000°C. The spectrum is characterized by absorption lines of neutral or singly ionized helium, with lines of atomic hydrogen evident, especially at the cooler end of the range.
Main sequence B stars, examples of which include Spica and Regulus, have a mass in the range 3 to 20 solar masses and a luminosity of 100 to 50,000 times that of the Sun. Often they are found together with O stars in OB associations since, being massive, they are short-lived and therefore do not survive long enough to move far from the place where they were formed. Their brief main sequence careers, measured in tens of millions of years, probably allows too little time for even the most primitive forms of life to develop on any worlds that circle around them (assuming that life could exist at all in such an environment).
B-type supergiants, of which Rigel is a familiar example, may be up to 25 times as massive and 250,000 times as luminous as the Sun.