Here's why:

* Betelgeuse is a red supergiant: This means it's a much larger and more massive star than our Sun.

* Surface temperature: Betelgeuse's surface temperature is around 3500 Kelvin (K), while the Sun's surface temperature is about 5778 K.

* Spectral type: Betelgeuse is a red supergiant (spectral type M2), which indicates a cooler surface temperature compared to our Sun, which is a yellow dwarf (spectral type G2). However, even though it's cooler than the Sun, its core is much hotter due to its larger size and mass.

Even though Betelgeuse has a cooler surface, the overall energy output of Betelgeuse is much greater than our Sun. This is because it's a much larger star.