As an expert in the field of astronomy, I can provide you with information on the hottest stars known. The temperature of a star is determined by its spectral type, with the hottest stars being those of the O and B spectral classes. The hottest known main-sequence star is Epsilon Eridani, which is a K-type star, not the hottest but still quite warm. However, when considering the most extreme stars, the Wolf-Rayet stars are among the hottest, with surface temperatures exceeding 200,000 Kelvin (K). These are evolved, very massive stars that are nearing the end of their life cycle. The most extreme and hottest observed star to date is R136a1 in the Large Magellanic Cloud, with an estimated surface temperature of over 45,000 K.

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If a star looks red, that means its surface temperature is approximately 2,500 Kelvin. Just for comparison, our Sun, which actually looks white from space, measures about 6,000 Kelvin. The hotter the star, the further up the spectrum you go. The hottest stars are the blue stars.read more >>