Relative size of O-type stars with other main-sequence stars
An O-type star is a hot, blue-white star of spectral type O in the Yerkes classification system employed by astronomers. They have temperatures in excess of 30,000 kelvins (K). Stars of this type have strong absorption lines of ionised helium, strong lines of other ionised elements, and hydrogen and neutral helium lines weaker than spectral type B.
https://en.wikipedia.org/wiki/Elephant%27s_Trunk_Nebula
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