O - type star

O - type stars are the hottest of all. They have strong solar winds and deadly radiations and may possess only a theoretical Habitable Zone.

The star
Even if they have the strongest luminosity, these stars are extremely rare. The brightest star of them all, R136a1, is a million times as bright as our sun, Sol. Their lifetime is extremely short, after this they will explode as supernovas and will become black holes. Also known as Wolf - Rayet stars, their solar wind is so powerful that they lose matter a billion times faster then Sol, through solar wind. Blowing away all their energy fast, these stars will last not much above 10 million years.

Light composition is different from what a habitable star has. The largest part of their radiation is in far ultraviolet and also in x-ray. Deadly, this radiation will kill any existing organism. Visible light is mostly emitted in blue and is less then 10%.