There isn't a single "hottest star" in the universe that we know of. The hottest stars are classified as O-type stars. These stars are incredibly massive, burning through their fuel very quickly, and have surface temperatures exceeding 30,000 Kelvin (53,540° Fahrenheit).

Here's why finding a definitive "hottest" is tricky:

* We can only observe a limited portion of the universe. There might be even hotter stars beyond our current observation capabilities.

* Stars are constantly evolving. A star's temperature can change significantly throughout its lifetime.

Some examples of exceptionally hot stars:

* R136a1: This is the most massive star known, located in the Tarantula Nebula. It has a surface temperature estimated at around 50,000 Kelvin.

* WR104: This Wolf-Rayet star is incredibly hot and is thought to be a potential candidate for a future supernova.

Ultimately, while we can identify incredibly hot stars, finding the absolute hottest star in the vastness of the universe is a challenge that may not be possible with our current understanding and technology.