Here's why:

* Nuclear Fusion: The Sun's core is where nuclear fusion takes place. This is the process where hydrogen atoms fuse together to form helium, releasing immense amounts of energy.

* Extreme Temperatures: The incredible pressure and density within the core create temperatures that can reach 15 million Kelvin (27 million degrees Fahrenheit). While not quite 100 million K, it's still incredibly hot.

* No Direct Measurement: It's important to note that we can't directly measure the temperature of the Sun's core. Scientists use models and indirect observations to estimate its temperature.

Let me know if you have any other questions about the Sun!