White dwarfs are unimaginably dense -- 1014 [a hundred trillion] grams per cubic centimeter -- but their atmosphere [may] allow [for] mobility. Those atmospheres contain oxygen and carbon, and although they are quite cold, they are warm enough that they would allow those chemicals to interact in interesting ways. White dwarf atmospheres gain what heat they have by collisions with particles of dark matter, a process that will continue until the dark matter is exhausted, when the universe is 1025 years of age. Over such as span -- 100 billion times as long as it took for life to appear on Earth -- even slow-moving molecules have time to join in every conceivable pattern, including those necessary for life. The longevity of a stable environment...implies that life in white dwarf atmospheres is more than possible; it is likely...[It] would also be life quite unlike our own...metabolisms and rates of consciousness would be very slow. An intelligent creature living in a white dwarf atmosphere might take a thousand years to complete a single thought.-- from Weird Life by David Toomey
Borges includes Thermal Beings in his Book of Imaginary Beings. These are imagined to have existed in an earlier era.
See also White Dwarfs Hold Key to Finding Secret to Extraterrestrial Life