Here's why:

* Nuclear Fusion: The core is where nuclear fusion takes place, converting hydrogen into helium. This process releases immense energy and creates a tremendous pressure.

* Gravity: The immense gravity of the Sun pulls all of its mass inward, squeezing the core to an incredibly high density.

* Temperature: The core is the hottest part of the Sun, reaching temperatures of around 15 million degrees Celsius (27 million degrees Fahrenheit). This high temperature further contributes to the density.

While the exact density of the core is difficult to determine precisely, it's estimated to be around 150 times denser than water. This means a teaspoon of Sun's core would weigh about 150 kilograms (330 pounds) on Earth!