Talk:Black dwarf

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[edit] Black body radiation

This entry used to say: "only emits black-body radiation". But black body radiation can be bright white; the "black-body" refers to the fact taht the body doesn't reflect light--all the light it emits it generates itself. A white dwarf is as much (or as little) of a black body as a black dwarf. -- —The preceding unsigned comment was added by 24.6.67.123 (talk • contribs).

[edit] Black dwarfs in other universes

Removed "It is possible, though, that some black dwarfs currently exist in other universes that are old enough to have them, if they exist." Pretty much anything is possible when you invoke other universes, so this doesn't add anything to the reader's understanding of black dwarfs. -- JustSayin 18:13, 7 April 2006 (UTC)

"Other Universe"?O.o —The preceding unsigned comment was added by 68.237.238.121 (talk • contribs) on 02:29, 1 May 2006.

Depending on what assumptions you make about how cosmic inflation works, or how m theory works, you can get laws of physics that allow "other universes" to exist (universe-like spaces that are not in causal contact with our own). Under some situations, these may have existed for far longer than our own universe, raising the possibility of burned-out stars cooling to become black dwarfs (which hasn't yet occurred in our universe). As was pointed out above, you can postulate just about any scenario you like existing in other universes, so it isn't usually a terribly useful exercise. --Christopher Thomas 22:52, 2 May 2006 (UTC)

[edit] Colonizing a black dwarf

Something I've been vaguely curious about for a while: whenever the time comes that we do get black dwarfs, would it be "possible" to land future astronauts on them? What would the ground be like? Could we actually colonize these... dead stars as planets? —The preceding unsigned comment was added by 72.60.109.138 (talk • contribs) on 00:30, 11 June 2006.

A black dwarf would be a ball of mostly carbon, nitrogen, and oxygen. If I understand correctly, most of the nuclei would be in a spherical close-pack crystalline lattice (most space-efficient possible), with the degenerate electron gas permeating through the lattice. This would form a metallic core of the star. Close to the surface, you still get a close-packed lattice, but some of the electrons are bound to individual nuclei. Very close to the surface, you get something resembling normal matter (carbon, nitrogen, and oxygen compressed enough to become metallic and share valence electrons, but not compressed enough to lose core electrons). Above this would be a thin layer of carbon nitride, diamond, and other compounds with more normal crystal structures. The atmosphere would be hydrogen and helium with trace amounts of water, methane, and ammonia.

Colonizing a world like this would be difficult, mostly due to the extremely strong surface gravity. A Newtonian approximation gives something like 200,000 times Earth's gravity, but the actual result will be very different. The gravity well is deep enough to require General Relativity for a full description; Newtonian gravity gives an escape velocity greater than the speed of light. Humans would be instantly crushed, and any kind of structure would have to be very small (less than a millimetre high gives the kinds of stresses found in the tallest existing buildings). A more viable approach with today's technology would be to find a white dwarf that hadn't quite cooled to the black dwarf stage, and build a dyson swarm of habitats around it.

It would make a nifty science fiction story, though. See Dragon's Egg for a similar story about a neutron star. --Christopher Thomas 19:42, 11 June 2006 (UTC)

Thanks a lot, Mr. Thomas. You've answered a question I've wondered about since I was a young lad, nose deep in outdated astronomy books. :) Nerva 16:34, 16 June 2006 (UTC)

Just caught a mistake I'd made: The black dwarf would be almost completely carbon. The CNO cycle transmutes existing carbon into nitrogen and oxygen (and then carbon again), but that would only cycle carbon that was present when the star formed, during hydrogen burning. Most of the white dwarf's carbon would be formed later via the triple-alpha process during helium burning. --Christopher Thomas 16:25, 27 June 2006 (UTC)