3 Characteristics of O-Type Stars

Most stars are listed under the Morgan-Keenan system that utilizes the letters O, B, A, F, G, K, M, L, T, and Y. This series ranges from the hottest (O type) to the coolest (Y) type. The kinds R and N are carbon-based stars; the type S is zirconium-monoxide-based stars. Each letter in this sequence is further subdivided using a numeric digit with zero being the hottest and nine being the coolest–forming a chain from more blistering to coldest.

What is an O-Type Star?

An O-type star is a hot, blue-white star in the MKK classification system employed by astronomers. They have temperatures over 30,000 kelvin (K). Stars of this type have sharp absorption lines of ionized helium, strong lines of other ionized elements, and hydrogen and neutral helium lines weaker than type B. In simpler terms, O-type stars are the hottest of its kind in the Universe. Our sun averages under 6000K, around five times lesser than the O-type stars. 

Here are three characteristics of O-Type Stars


O-type main-sequence stars are fired by nuclear fusion, as all main-sequence stars are. However, the great mass of O-type stars results in remarkably high core temperatures. At these heats, hydrogen fusion with the CNO cycle controls the production of the star’s energy. It consumes its nuclear fuel at a much more unusual rate than low-mass stars, which fuse hydrogen with the proton-proton cycle. The excessive amount of heat generated by O-type stars cannot be transmitted out of the core efficiently enough, and consequently, they undergo displacement in their centers. The radiative zones of O-type stars occur between the base and photosphere. This mixing of core material into the higher layers is often magnified by high-speed rotation and has a climactic effect on O-type stars’ evolution. 


In the O-type stars’ lifecycle, various metallicities and rotation rates introduce considerable variation in their evolution, but the basics remain similar. O-type stars start to move from the zero-age main sequence almost immediately, becoming progressively colder and slightly more bright. Although they may be distinguished spectroscopically as giants or supergiants, they keep on burn hydrogen in their cores for several million years. They evolve in a very different manner from low-mass stars such as our Sun. Most O-type main-sequence stars will develop more or less horizontally in the HR diagram to colder temperatures, becoming blue supergiants. Core helium ignition occurs evenly as the stars expand and cool. Several complex phases depend on the exact mass of the star and other initial conditions. However, the lowest mass O-type stars will ultimately evolve into red supergiants while still burning helium in their cores. Suppose they do not explode as a supernova first. In that case, they will lose their exterior layers and become hotter again, sometimes going through several blue loops before finally reaching the Wolf–Rayet stage.


Many experts argue that O-class stars live too short to settle planets. Their mighty solar wind can blow away a wandering disk. However, if a planet is captured and sadly gets into orbit around such a star or gets formed somehow, it will encounter various problems. O-type stars radiate mainly far-UV light that will destroy the atmosphere of any planet trapped in this mighty burning delight. Solar winds on O-types are nearly 100 times more massive than other stars, and this will shatter any object around it. Another issue is that the star is continually losing mass. As this happens, gravity decreases, and planets move outwards until they are thrown away in deep space.

Was it worth reading? Let us know.