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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 b

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.

surgical_fire 2y ago
At 1/100 distance, wouldn't a hypothetical planet be tidally locked to the white dwarf? Could tidally locked planets be suitable for life?
- cenamus 2y ago
  Not quite that close but Mercury seems to have an interesting interaction with the sun https://en.m.wikipedia.org/wiki/Mercury_(planet)#Spin-orbit_resonance https://en.m.wikipedia.org/wiki/Mercury_(planet)#Spin-orbit_...
- A_D_E_P_T 2y ago
  > At 1/100 distance, wouldn't a hypothetical planet be tidally locked to the white dwarf? Probably. Well, usually. If something gave that planet a very hard knock, it could spin up for a while, especially if it's around the outer limits of the proposed habitable zone. > Could tidally locked planets be suitable for life? Definitely. Depends how well they're able to redistribute heat from the hot side to the dark side. So atmospheric composition and water content (also the presence and extent of surface water) would be the decisive factors. You'd get wild weather, though.
  - 867-5309 2y ago
    it's a hard knock white dwarf dust
    - Loughla 2y ago
      That's almost a joke. I don't know what to categorize that as. It isn't a pun. What is that?
      - bovermyer 2y ago
        It's technically a filk, just really short.
      - thehappypm 2y ago
        “It’s a hard knock white.. dwarf dust!” Is the joke
        Loughla 2y ago
        Yes. I understand. I was saying it's almost a joke. But for real what is it called when the things you're saying don't necessarily rhyme with the original phrase but have a similar cadence?
        thehappypm 2y ago
        This does (nearly) rhyme
  - bell-cot 2y ago
    > Definitely. Depends how well... I'm less optimistic. Between the fraction of the planet's surface that's suitable for life, the lack of tides, the (likely) lack of plate tectonics, and impairment of the various cycles ( https://en.wikipedia.org/wiki/Biogeochemical_cycle https://en.wikipedia.org/wiki/Biogeochemical_cycle ) - tidal locking to the star will profoundly degrade the planet's suitability for life. Tidal locking may also rule out having a planetary magnetic field. Though "protect the atmosphere" may not matter much, if said atmosphere (plus the water) has all condensed and frozen on the dark side of the planet.
- BurningFrog 2y ago
  On a tidal locked planet, conditions should be very static. The point facing the sun is the hottest, and the opposite point is the coldest. Which means there is a constant "spectrum" of climates in between, and you only need one of these thousands of microclimates to be beneficial for creating life. So this may be the planets most suitable for life, if this theory I just made up has any validity!
  - surgical_fire 2y ago
    It does make some sense, even if life would be viable only in (for example) the twilight rim of the planet (such as around the poles)
  - cma 2y ago
    https://en.wikipedia.org/wiki/Eyeball_planet https://en.wikipedia.org/wiki/Eyeball_planet
- rybosome 2y ago
  I once read an article that speculated about this. The conclusion was that perhaps there could be a ring around the planet, at the border of the side facing the sun from the side facing away from the sun. That ring could be a habitable zone.
- AnotherGoodName 2y ago
  A large moon should absolutely mess this tidal locking up fwiw since it will have far more influence than the star just as our moon has far more tidal influence than our sun. Not that I think tidal locking is a blocker for life but it’s also not a big deal since large moons are extremely common and therefore the tidal locking is not guaranteed.
khuey 2y ago
> All of this can happen via quantum processes at zero temperature. So they end as lumps of indefinitely stable cold iron. Assuming no proton decay, of course.
- A_D_E_P_T 2y ago
  Which has yet to be experimentally observed. At some point we'll be able to rule it out, I'm sure.
  - jahnu 2y ago
    Sorry if this is a stupid question. If proton decay does not happen, but a proton is say in motion through a galaxy, where does the energy for its gravitational waves come from? Its momentum and therefore it slows down?
    - A_D_E_P_T 2y ago
      A lone proton coasting inertially through empty space at a constant velocity, even if it's moving quickly, does not generate any gravitational waves. It might generate gravitational waves if it's accelerated, but then those would come from the energy budget responsible for that acceleration.
      - justsomeshmuck 2y ago
        Is it only accelerating objects that emit gravity waves/particles, or do decelerating objects do it too?
        ChrisClark 2y ago
        That's the same thing
        soulofmischief 2y ago
        Acceleration is a general term for both increases and decreases in velocity. It might also surprise you to know that "incline" functions the same way.
api 2y ago
What I love about the idea of planetary systems around dwarf stars is that if the planets were close it would make interplanetary flight quite a bit faster and easier. Now imagine multiple ones with life. Someone out there in the vastness of the cosmos might be LARPing Buck Rogers or Commando Cody. Simple rockets could take you everywhere. It’d be like The Expanse but without the physicists nightmare fusion torches. Such things can maybe be built but it’s many orders of magnitude harder. These folks could be living the dream with 1950s level tech. They probably look like crabs though.
- wruza 2y ago
  Also due to tidal lock “weather” they can simply kite their satellites (and rockets/missiles) to the orbit, for the most part. You open the hatch and let it fly. Don’t forget to close the hatch though, or your entire dream will fly too.
  - api 2y ago
    Whoa… I never thought of that. If complex life were possible on a tide locked planet that held onto its atmosphere you could ride the powerful currents this would create at least much of the way to orbit. You’d probably need a rocket to reach orbital velocity and escape but the atmosphere might be almost like your first rocket stage. Such a civilization would also have endless free energy via solar harnessed from the sun side and continuous prevailing powerful winds. The latter would probably get tapped first. Huge wind turbines would just always spin. This would be true from their dawning of industry, which would be interesting. No energy wars. I’m sure they’d find something else to fight about if they were aggressive and territorial like us.
    - cruffle_duffle 2y ago
      Wouldn’t the amount of habitable land mass on a tidal locked planet be rather small? Like the bulk of the planet is either hotter than hells freezer or colder than its hot tub. You’ve got only a fixed ring of land that would be usable. Unless life can survive & thrive in the remainder. Which I’m sure it can and does.
jajko 2y ago
Wouldn't gravity tidal forces rip those planets eventually apart? Like we expect ie Phobos to end up, and Mars has much gentler gravity gradient than this would have. Or would tidal locking somehow prevent it?
- wiml 2y ago
  I think even for a white dwarf the Roche limit is well inside the inner edge of the habitable range. So a planet that gets torn apart by gravity would already have been uninhabitably close.
pavel_lishin 2y ago
> Intelligent life can hang around white dwarfs for a long time. Good candidate star type for Dyson spheres. I would imagine that if intelligent life can build a Dyson sphere, it can probably travel to different stars as well.

surgical_fire 2y ago

At 1/100 distance, wouldn't a hypothetical planet be tidally locked to the white dwarf? Could tidally locked planets be suitable for life?

cenamus 2y ago
Not quite that close but Mercury seems to have an interesting interaction with the sun https://en.m.wikipedia.org/wiki/Mercury_(planet)#Spin-orbit_resonance https://en.m.wikipedia.org/wiki/Mercury_(planet)#Spin-orbit_...
A_D_E_P_T 2y ago
> At 1/100 distance, wouldn't a hypothetical planet be tidally locked to the white dwarf? Probably. Well, usually. If something gave that planet a very hard knock, it could spin up for a while, especially if it's around the outer limits of the proposed habitable zone. > Could tidally locked planets be suitable for life? Definitely. Depends how well they're able to redistribute heat from the hot side to the dark side. So atmospheric composition and water content (also the presence and extent of surface water) would be the decisive factors. You'd get wild weather, though.
- 867-5309 2y ago
  it's a hard knock white dwarf dust
  - Loughla 2y ago
    That's almost a joke. I don't know what to categorize that as. It isn't a pun. What is that?
    - bovermyer 2y ago
      It's technically a filk, just really short.
    - thehappypm 2y ago
      “It’s a hard knock white.. dwarf dust!” Is the joke
      - Loughla 2y ago
        Yes. I understand. I was saying it's almost a joke. But for real what is it called when the things you're saying don't necessarily rhyme with the original phrase but have a similar cadence?
        thehappypm 2y ago
        This does (nearly) rhyme
- bell-cot 2y ago
  > Definitely. Depends how well... I'm less optimistic. Between the fraction of the planet's surface that's suitable for life, the lack of tides, the (likely) lack of plate tectonics, and impairment of the various cycles ( https://en.wikipedia.org/wiki/Biogeochemical_cycle https://en.wikipedia.org/wiki/Biogeochemical_cycle ) - tidal locking to the star will profoundly degrade the planet's suitability for life. Tidal locking may also rule out having a planetary magnetic field. Though "protect the atmosphere" may not matter much, if said atmosphere (plus the water) has all condensed and frozen on the dark side of the planet.
BurningFrog 2y ago
On a tidal locked planet, conditions should be very static. The point facing the sun is the hottest, and the opposite point is the coldest. Which means there is a constant "spectrum" of climates in between, and you only need one of these thousands of microclimates to be beneficial for creating life. So this may be the planets most suitable for life, if this theory I just made up has any validity!
- surgical_fire 2y ago
  It does make some sense, even if life would be viable only in (for example) the twilight rim of the planet (such as around the poles)
- cma 2y ago
  https://en.wikipedia.org/wiki/Eyeball_planet https://en.wikipedia.org/wiki/Eyeball_planet
rybosome 2y ago
I once read an article that speculated about this. The conclusion was that perhaps there could be a ring around the planet, at the border of the side facing the sun from the side facing away from the sun. That ring could be a habitable zone.
AnotherGoodName 2y ago
A large moon should absolutely mess this tidal locking up fwiw since it will have far more influence than the star just as our moon has far more tidal influence than our sun. Not that I think tidal locking is a blocker for life but it’s also not a big deal since large moons are extremely common and therefore the tidal locking is not guaranteed.

khuey 2y ago

> All of this can happen via quantum processes at zero temperature. So they end as lumps of indefinitely stable cold iron. Assuming no proton decay, of course.

A_D_E_P_T 2y ago
Which has yet to be experimentally observed. At some point we'll be able to rule it out, I'm sure.
- jahnu 2y ago
  Sorry if this is a stupid question. If proton decay does not happen, but a proton is say in motion through a galaxy, where does the energy for its gravitational waves come from? Its momentum and therefore it slows down?
  - A_D_E_P_T 2y ago
    A lone proton coasting inertially through empty space at a constant velocity, even if it's moving quickly, does not generate any gravitational waves. It might generate gravitational waves if it's accelerated, but then those would come from the energy budget responsible for that acceleration.
    - justsomeshmuck 2y ago
      Is it only accelerating objects that emit gravity waves/particles, or do decelerating objects do it too?
      - ChrisClark 2y ago
        That's the same thing
      - soulofmischief 2y ago
        Acceleration is a general term for both increases and decreases in velocity. It might also surprise you to know that "incline" functions the same way.

api 2y ago

What I love about the idea of planetary systems around dwarf stars is that if the planets were close it would make interplanetary flight quite a bit faster and easier. Now imagine multiple ones with life. Someone out there in the vastness of the cosmos might be LARPing Buck Rogers or Commando Cody. Simple rockets could take you everywhere. It’d be like The Expanse but without the physicists nightmare fusion torches. Such things can maybe be built but it’s many orders of magnitude harder. These folks could be living the dream with 1950s level tech. They probably look like crabs though.

wruza 2y ago
Also due to tidal lock “weather” they can simply kite their satellites (and rockets/missiles) to the orbit, for the most part. You open the hatch and let it fly. Don’t forget to close the hatch though, or your entire dream will fly too.
- api 2y ago
  Whoa… I never thought of that. If complex life were possible on a tide locked planet that held onto its atmosphere you could ride the powerful currents this would create at least much of the way to orbit. You’d probably need a rocket to reach orbital velocity and escape but the atmosphere might be almost like your first rocket stage. Such a civilization would also have endless free energy via solar harnessed from the sun side and continuous prevailing powerful winds. The latter would probably get tapped first. Huge wind turbines would just always spin. This would be true from their dawning of industry, which would be interesting. No energy wars. I’m sure they’d find something else to fight about if they were aggressive and territorial like us.
  - cruffle_duffle 2y ago
    Wouldn’t the amount of habitable land mass on a tidal locked planet be rather small? Like the bulk of the planet is either hotter than hells freezer or colder than its hot tub. You’ve got only a fixed ring of land that would be usable. Unless life can survive & thrive in the remainder. Which I’m sure it can and does.

jajko 2y ago

Wouldn't gravity tidal forces rip those planets eventually apart? Like we expect ie Phobos to end up, and Mars has much gentler gravity gradient than this would have. Or would tidal locking somehow prevent it?

wiml 2y ago
I think even for a white dwarf the Roche limit is well inside the inner edge of the habitable range. So a planet that gets torn apart by gravity would already have been uninhabitably close.

pavel_lishin 2y ago

> Intelligent life can hang around white dwarfs for a long time. Good candidate star type for Dyson spheres. I would imagine that if intelligent life can build a Dyson sphere, it can probably travel to different stars as well.