Class B — B-type (Blue-White)

B-type stars are very hot and luminous blue-white stars with surface temperatures between 10,000 and 30,000 K. They are relatively rare, making up about 0.13% of main-sequence stars. B-type stars are prominent members of young open clusters and OB associations. Many of the brightest stars visible to the naked eye are B-type, including Rigel (B8Ia), Spica (B1V), and Regulus (B8IVn). They live for tens to hundreds of millions of years.

B-type stars are among the most visually striking objects in the night sky, combining high luminosity with a distinctive blue-white color. With surface temperatures between 10,000 and 30,000 K and masses from 2 to 16 solar masses, they are far more common than O-types while still being rare compared to cooler stars — roughly 0.13% of main-sequence stars. Many of the brightest stars visible to the naked eye are B-type, making them disproportionately important in defining constellation patterns.

Characteristics

B-type spectra are characterized by neutral helium (He I) absorption lines, which reach maximum strength at B2. Hydrogen Balmer lines are also prominent. B stars have lifetimes of 10-500 million years — long enough to drift from their birthplace but short enough that they still trace spiral arm structure. Many B stars are rapid rotators, with equatorial velocities exceeding 200 km/s. The Be stars (B-emission) are a fascinating subclass that eject matter into circumstellar disks, producing emission lines that can appear and disappear over years.

Notable Examples

Rigel (Beta Orionis, B8Ia) is the quintessential blue supergiant — the seventh-brightest star in the sky, shining at 120,000 solar luminosities from 860 light-years away. Spica (Alpha Virginis, B1III) is a close binary whose components nearly touch. The Pleiades (Seven Sisters) are dominated by hot B-type stars wrapped in reflection nebulosity. Achernar (Alpha Eridani, B6Vep) is one of the flattest stars known — its rapid rotation distorts it into an oblate shape 56% wider at the equator.

HIP 77761HIP 77764HIP 30961HIP 7780HIP 77800HIP 87574HIP 77862HIP 34196HIP 34203HIP 99036HIP 31017HIP 31019HIP 77911HIP 77918HIP 85595HIP 77976HIP 8020HIP 57097HIP 78034HIP 78046HIP 87758HIP 87798HIP 78168HIP 96097HIP 86023HIP 86031HIP 86076HIP 8609HIP 86146HIP 78279HIP 31113HIP 31115HIP 97982HIP 78306HIP 78310HIP 5813HIP 38457HIP 38467HIP 38469HIP 38470HIP 80552HIP 80557HIP 58015HIP 38498HIP 31190HIP 31195HIP 31196HIP 31199

Frequently Asked Questions

What is a class B star?
Class B (B-type (Blue-White)) stars are blue-white stars. B-type stars are very hot and luminous blue-white stars with surface temperatures between 10,000 and 30,000 K. They are relatively rare, making up about 0.13% of main-sequence stars. B-type stars are
How hot are class B stars?
Class B stars have surface temperatures between 10,000 K and 30,000 K.
What color are class B stars?
Class B stars appear blue-white.
How many class B stars are in the StarFYI database?
StarFYI currently catalogs 10,413 class B stars.
How luminous are class B stars?
Very luminous, 25-30,000 solar luminosities