Caption: Click on image and then click on the video to see---after a preliminary view of the Sun as a red giant???---a white dwarf aging from being a newly formed white white dwarf (WD) to being on its way to being black dwarf after some gigayears (Gyr).

Features:

1. White dwarfs have NO nuclear burning to replenish the heat energy they radiate away from their photospheres as electromagnetic radiation (EMR).

   So they can only lose heat energy and cool off forever.

   They do constract a little as they cool, and so some gravitational potential energy gets converted to heat energy, but this is a minor source of heat energy.????

2. Eventually white dwarfs will drop to such low temperatures that they mainly radiate at wavelengths longer than the visible. They then radiate mainly in the infrared, later mainly in the microwave, and then later mainly in the radio. Once they stop radiating mainly in visible, they are called black dwarfs.

   Note the definition of black dwarf given here is NOT used universally. The stage of transition from white dwarf to black dwarf may be defined differently by different authors.

3. The white dwarf cooling time is very long---many billions of years. Since the Big Bang, NO white dwarf has cooled off to become a black dwarf it is thought.

   It always astounds yours truly that we know there are astronomical objects that will exist in the cosmologically far future---if the observable universe ever gets to the cosmologically far future---that have never existed before in the observable universe.

4. The coldest existing white dwarfs have photospheric temperatures of ∼ 4000 K (see Wikipedia: White dwarf: Radiation and cooling).

5. By the way, white dwarfs do have stellar atmospheres, and so do NOT necessarily radiate like blackbody radiators at least at all phases though probably they do so to some crude approximation at all phases???? (see Wikipedia: White dwarf: Radiation and cooling). For an example of "NOT necessarily", note that strange opacity effects may lead to significant deviations from being approximate blackbody radiators when their photospheric temperature is < ∼6000 K (e.g., Kowalski, Saumon, et al., 2013).???