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What is the Density of a White Dwarf?

-- Heraldo Henrique Felix de Moraes | May 9, 2021

Question:

Hello, I have some doubts about the White Dwarfs, the first is in relation to its density, what is the density of a White Dwarf? I saw on Wikipedia, in Portuguese that, on average 109 kg / cm3; in some cases, it can reach 10 000 kg / cm3, and in Wikipedia in English, between 100 kg / cm³ and 10 tons / cm³ these values refer to the average density, or on the surface, for example, the density would be lower, as occurs with the Sun, our planet or even the neutron stars? Does the density vary according to the mass of the White Dwarf? And how can a White Dwarf be so dense, since they are basically composed of carbon and oxygen?
Another question of mine is about the final stage of these stars, the Black Dwarfs, would they still have such a high density? Would they be a very dense and cold celestial body, or would it be a cold but low density object?

-- Heraldo Henrique Felix de Moraes

Answer:

According to the description of the properties of a White Dwarf from NASA, an Earth-sized white dwarf has a density of 10^9 kg/m^3. As this description notes, a White Dwarf has a layered crust with a thin atmosphere above it and a crystalline lattice of carbon and oxygen atoms below the crust. This crystalline lattice of carbon and oxygen has often been compared to the structure that one finds in a diamond on Earth. This density structure would persist through the Black Dwarf stage as long as there are no changes in its density (i.e. through a process of mass accretion from a companion).

-- Jeff Mangum

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