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A star that is bright, gives off blue light, and can have a world that mimics conditions on Earth is tricky. I'm hoping I can get one around a blue-colored white dwarf star.

What does the arrangement of this star system look like? Please give an idea of how the planetary rotation and orbital mechanics would need to work. If there are clear reasons this CAN'T work, a frame challenge is acceptable.

I want to have a human-habitable planet in orbit around a blue-colored white dwarf star. Life does not need to evolve in this system, just exist there for a reasonable timeframe (the planet can come from elsewhere via handwavium). The star should currently appear bright in the sky, and the planet should have a real or apparent day-night cycle somewhere between 20-30 hours (the planet can be tidally locked or nearly tidally locked, but if so, explain how do you achieve a day/night cycle).The planet needs to be in this location and in at least close to this condition for at least a million years prior (longer would be preferred, 65 million years is ideal).

Beyond that, the sky is the limit.

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    $\begingroup$ You're asking too many questions. One at a time. Can a white dwarf even be hot enough to give blue-tinted light like Vega or Sirius A? How long will it stay that hot? How big is the habitable zone if so? How long does tidal locking take? $\endgroup$
    – Zeiss Ikon
    Oct 13, 2022 at 17:46
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    $\begingroup$ @ZeissIkon White dwarf stars can range from blue to near yellow because they are the slowly cooling core from a sun. en.wikipedia.org/wiki/White_dwarf It's one question - the orbit of a specific planet around a specific kind of star with specific conditions. Breaking it up would make it LESS specific, and I thought the point was to make a question that can have a right or wrong answer. $\endgroup$
    – DWKraus
    Oct 13, 2022 at 18:06
  • $\begingroup$ There will be no day-night cycle on your world. The side facing the star will be in perpetual daylight and the side facing away from the star will be in perpetual nighttime $\endgroup$
    – Slarty
    Oct 13, 2022 at 19:54
  • $\begingroup$ @Slarty Please give that as your answer. I'll take a frame challenge if no one can think of a way around it. $\endgroup$
    – DWKraus
    Oct 13, 2022 at 21:35
  • $\begingroup$ @DWKraus Please remember that the help center states to avoid closure you shouldn't give your own answers and expect more. The point of that rule is that you have an answer, so why bother asking here? You can't use brainstorming as an excuse, that's forbidden, too (help center). So, why don't you like your answer? Why is it insufficient? $\endgroup$
    – JBH
    Oct 16, 2022 at 0:06

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Blue is definitely possible. The Hertzsprung-Russell shows the top end of the white dwarf range being as blue as the lower end of O stars. Such a star has about 1% of the luminosity of the sun, thus your planet is roughly 9.3 million miles from it.

For the star to be that hot this must be a fairly new situation (your star is going to cool over time, it won't stay blue forever), tidal locking might not have occurred yet.

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Instead of having your planet orbiting a white dwarf (with all the difficulties, like impossibility to survive the red giant phase), consider using a blue dwarf - evolved red dwarfs in their post-main sequence stage. There is a lot of uncertainty, but something like $0.17 M_\odot$ star can reach surface temperature of 8000 K (definitely blueish) and achieve the luminosity from $0.1L_\odot$ up to $0.3L_\odot$ in some billions of years, definitely enough for the life to evolve, and $0.3L_\odot$ means the planet would be 0.55 AU from the star - i.e. somewhat closer than Venus to the Sun. Definitely no need for tidal locking (but some handwaving necessary to explain why it did not became tidally locked during the main sequence era).

This means the story takes place in a far, far future.

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  • $\begingroup$ Note that planets have been observed around pulsars, so if a planet can survive a supernova, then surviving a red giant is a piece of cake compared to that $\endgroup$
    – Seggan
    Jul 3, 2023 at 1:59
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There will be no day-night cycle on your world. The side facing the star will be in perpetual daylight and the side facing away from the star will be in perpetual nighttime.

This is why we always see the same* face of the Moon from Earth

Actually around 59% of the Moon can be seen from time to time due to the various forms of liberation caused by parallax, eccentricity and various other causes. https://en.wikipedia.org/wiki/Libration#

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