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A comment on We've spotted a planet surviving its dying star. Parent comment

Re:We've spotted a planet surviving its dying star by Chris2048 on Friday October 15, 2021 @08:42AM (#28877093)
A BD is still hotter than background temp, so you could maybe see faint IR, and you could initially find it as a result of its mass if there are nearby objects orbiting (although now less illuminated), or simply transitioning in front of other stars (I guess that's how they find wandering planets?).

Alternatively, map all the white dwarves, then wait long enough, then look again..

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Re:We've spotted a planet surviving its dying star by kadoban on Friday October 15, 2021 @09:28AM (#28877458)
You'd probably also be able to see white dwarves that were on their way to being black (whatever the threshold is).
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Re:We've spotted a planet surviving its dying star by Chris2048 on Friday October 15, 2021 @01:14PM (#28880221)
Given there are no BDs (so they are theoretical) maybe there isn't a threshold defined?

A WD will slowly cool to a BD over Trillions of years, so it's all linear. Funnily enough, they are probably every shade of red/brown in-between - but "brown dwarves" are usually reserved for objects that never where "proper" hydrogen-fusing stars, but are large enough to fuse deuterium.

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Re:We've spotted a planet surviving its dying star by kijin on Friday October 15, 2021 @12:20PM (#28879487)
There's no hard threshold, the star just fades gradually from #FFF to #000.

A fully black dwarf would be so cold it would be indistinguishable from cosmic background radiation, but that's going to take at least a trillion times longer than the current age of the universe. Not just slightly longer.

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Re:We've spotted a planet surviving its dying star by kadoban on Friday October 15, 2021 @01:02PM (#28880084)
Right. I'm just saying that if the are any black dwarfs (which there should not be), we should be able to find ~arbitrarily dim ones as well, down to our ability to see.
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