Here's why:

* The Sun's core is the heart of the Sun: It's where nuclear fusion happens, converting hydrogen into helium and releasing tremendous amounts of energy.

* Extreme heat: The core reaches temperatures of about 27 million degrees Fahrenheit (15 million degrees Celsius).

* Surface comparison: The Sun's surface, called the photosphere, is much cooler, reaching temperatures of around 10,000 degrees Fahrenheit (5,500 degrees Celsius).

So, even though the Sun's surface is incredibly hot, the core is even hotter due to the intense nuclear reactions happening within it.