Why do sunspots appear as dark spots on the surface of the Sun?

Why do sunspots appear as dark spots on the surface of the Sun?

Sunspots are "dark" because they are cooler than their surroundings. ... Sunspots have a lighter outer section called the penumbra, and a darker central region named the umbra. Sunspots are caused by disturbances in the Sun's magnetic field welling up to the photosphere, the Sun's visible "surface".

Facts about the sun: The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy mainly as visible light, ultraviolet light, and infrared radiation. It is by far the most important source of energy for life on Earth.

Surface temperature: 5,778 K
Mass: 1.989 × 10^30 kg
Radius: 432,690 mi
Age: 4.603 billion years
Distance to Earth: 92.96 million mi
Spectral type: G2V
Moons: 3122 Florence, 90482 Orcus

The answer is constant.