As an expert in astrophysics, I can tell you that the concept of the "hottest star" can be a bit complex, as it depends on how we define "hot." In astronomy, the temperature of a star is often measured in Kelvins, and the hottest stars can reach temperatures of over 40,000 Kelvins. However, the hottest known star is not a main sequence star but rather a type of star nearing the end of its life cycle, known as a Wolf-Rayet star. These stars are extremely hot and luminous, with temperatures that can exceed 200,000 Kelvins.

Wolf-Rayet stars are typically found after a massive star has shed its outer layers and is left with a very hot core. One of the hottest stars known is the Wolf-Rayet star WR 102ka, which has been measured to have a temperature of over 200,000 Kelvins. It's important to note that the universe is vast and constantly evolving, so new discoveries may reveal even hotter stars in the future.

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Eta Carinae could be as large as 180 times the radius of the Sun, and its surface temperature is 36,000-40,000 Kelvin. Just for comparison, 40,000 Kelvin is about 72,000 degrees F. So it's the blue hypergiants, like Eta Carinae, which are probably the hottest stars in the Universe.read more >>