Category:Main Sequence O-type

An O-type main-sequence star (O V) is a main sequence (core hydrogen burning) star of spectral type O and luminosity class V. These stars have between 15 and 90 times the mass of Sol and surface temperatures between 30,000 and 50,000 K. They are between 40,000 and 1,000,000 times as luminous as Sol.

These are rare objects; it is estimated that there are no more than 20,000 class O stars in the entire Milky Way, around one in 10,000,000 of all stars. Class O main sequence stars are between 15 and 90 M☉ and have surface temperatures between 30,000 and 50,000 K. Their bolometric luminosities are between 30,000 and 1,000,000 L☉. Their radii are more modest at around 10 R☉. Surface gravities are around 10,000 times that of the Earth, relatively low for a main sequence star. Visual absolute magnitudes range from about −4, 3,400 times brighter than the sun, to about −5.8, 18,000 times brighter than the sun.

Class O stars are very young, no more than a few million years old, and in our galaxy they all have high metallicities, around twice that of the sun. O-type main sequence stars in the Large Magellanic Cloud, with lower metallicity, have noticeably higher temperatures, with the most obvious cause being lower mass loss rates. The most luminous class O stars have mass loss rates of more than a millionth M☉ each year, although the least luminous lose far less. Their stellar winds have a terminal velocity around 2,000 km/s.