Which type of supporting detail does the underlined sentence contain?

The hottest part of the sun is called the core. The core is at the center of the sun and is surrounded by the atmosphere. The core makes up about one-tenth the diameter of the sun, but it is the region where the sun's energy is generated. The temperature in the core may be as high as 15,000,000°C. The sun's energy is produced by nuclear fusion, a reaction in which small quantities of matter are converted to energy.