White dwarfs are characterized by their extreme density and compactness. They have masses roughly equal to that of the Sun but radii about 1% the size of the Sun, making them incredibly dense. A sugar-cube-sized amount of white dwarf material would have a mass of about a ton. This density is due to the degenerate electron pressure that supports them against further collapse. White dwarfs are also extremely hot when they first form, with surface temperatures around 100,000 Kelvin (180,000 degrees Fahrenheit), but they cool over time, eventually becoming black dwarfs, which are cold, dark, and nearly invisible.