Hmm. Interesting. A white dwarf is about the size of Earth -- roughly 1/100 the radius of the Sun. However, a planet in a white dwarf's habitable zone must be about 1/100 the Earth-Sun distance. (∼0.006 AU to ∼0.06 AU.) This dual scaling cancels out neatly. A white dwarf in that planet's sky would appear similar to the sun in our sky.
White dwarfs are also indefinitely stable; they keep cooling over billions of years to become black dwarfs. Then, over >10^100 years, all elements heavier than iron will decay to 56Fe by various processes such as fission and alpha emission. All atoms lighter than iron combine by nuclear fusion
reactions, building gradually up to 56Fe. All of this can happen via quantum processes at zero temperature. So they end as lumps of indefinitely stable cold iron.
Intelligent life can hang around white dwarfs for a long time. Good candidate star type for Dyson spheres.
A planet formed out of an accretion disk is generally a planet under continued bombardment from further accretion.
The only exception that we know of is our own Solar System. Where Jupiter acts like a vacuum cleaner to reduce material that might hit Earth. We knkw of no other system with both Earth-like planets and gas giants. Given how catastrophic the remaining asteroids have been for us (bye bye dinosaurs), this is unlikely to be a coincidence.
Unless we find a similar arrangement around a white dwarf, the time spent in the habitable zone isn't the only important factor for stability over evolutionary time frames.
I'd never seek to deprive anyone of entertaining alien-life theories, but in general people wildly underestimate the factors that play into making Earth habitable. The only evidence for a habitable planet-type is the very precise conditions that comprise this one. Worse, it's unclear as to how much those conditions rely on the complete configuration of the greater solar system.
A_D_E_P_T ·19 days ago
White dwarfs are also indefinitely stable; they keep cooling over billions of years to become black dwarfs. Then, over >10^100 years, all elements heavier than iron will decay to 56Fe by various processes such as fission and alpha emission. All atoms lighter than iron combine by nuclear fusion reactions, building gradually up to 56Fe. All of this can happen via quantum processes at zero temperature. So they end as lumps of indefinitely stable cold iron.
Intelligent life can hang around white dwarfs for a long time. Good candidate star type for Dyson spheres.
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btilly ·19 days ago
The only exception that we know of is our own Solar System. Where Jupiter acts like a vacuum cleaner to reduce material that might hit Earth. We knkw of no other system with both Earth-like planets and gas giants. Given how catastrophic the remaining asteroids have been for us (bye bye dinosaurs), this is unlikely to be a coincidence.
Unless we find a similar arrangement around a white dwarf, the time spent in the habitable zone isn't the only important factor for stability over evolutionary time frames.
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bookofjoe ·19 days ago
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mrangle ·19 days ago
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umanwizard ·18 days ago
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