[HN Gopher] Can life emerge around a white dwarf?
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Can life emerge around a white dwarf?
Author : JPLeRouzic
Score : 94 points
Date : 2024-12-07 08:02 UTC (14 hours ago)
(HTM) web link (www.centauri-dreams.org)
(TXT) w3m dump (www.centauri-dreams.org)
| A_D_E_P_T wrote:
| 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 wrote:
| 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 wrote:
| 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_...
| A_D_E_P_T wrote:
| > _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.
| bell-cot wrote:
| > 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 ) -
| 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.
| mapt wrote:
| Depending on the thickness and composition of the
| atmosphere, convection may be sufficient to prevent ice
| buildup.
|
| The thing about a tidally locked planet, and about
| marginally habitable planets in general, is that whatever
| the average, there are a wide range of surface conditions
| and often the spectrum is large enough that some subset
| of them are habitable.
| MichaelZuo wrote:
| Wouldn't the entire planet experience very high winds
| nearly all the time?
| tzs wrote:
| Does the atmosphere need protecting? White dwarfs don't
| have solar wind.
| 867-5309 wrote:
| it's a hard knock white dwarf dust
| Loughla wrote:
| That's almost a joke. I don't know what to categorize
| that as. It isn't a pun. What is that?
| bovermyer wrote:
| It's technically a filk, just really short.
| BurningFrog wrote:
| 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 wrote:
| 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)
| rybosome wrote:
| 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 wrote:
| 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 wrote:
| > 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 wrote:
| Which has yet to be experimentally observed. At some point
| we'll be able to rule it out, I'm sure.
| jahnu wrote:
| 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 wrote:
| 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 wrote:
| Is it only accelerating objects that emit gravity
| waves/particles, or do decelerating objects do it too?
| ChrisClark wrote:
| That's the same thing
| soulofmischief wrote:
| 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.
| jamiek88 wrote:
| Reminds me of a joke we have in racing, noobs often carry
| too much speed into a corner, reluctant to brake too much
| thinking that is quicker when in reality braking harder,
| earlier, often enables better lap time.
|
| To get over this mental hurdle we say 'it's not slowing
| down it's reaching your minimum speed faster!'
| anyfoo wrote:
| That still breaks my head. Reaching your minimum speed
| slower means you have a higher speed for a longer time,
| covering more distance?
|
| I know nothing about racing, is it maybe about reaching a
| _higher_ minimum speed by doing so before the curve?
| programjames wrote:
| Quite the opposite. Consider ------
| ------ \ / \ /
| \__/
|
| versus ------ ------ | |
| | | |_|
|
| The second is higher on average. If you're turning 90deg
| your velocity has to become zero in the direction you're
| going right now, so you might as well get there as fast
| as possible.
| anyfoo wrote:
| Ah, thanks. Here I thought that the distance that you're
| not driving at full speed would be equal in both cases,
| in which case you want to "minimize the minimum speed
| time", but the situation you present, where the distance
| you drive at minimum speed is equal, makes much more
| sense of course.
| hnuser123456 wrote:
| If you brake too late, you often end up going below the
| minimum speed to avoid going off the outside of the track
| when you find out your grip wasn't as much as you
| thought.
|
| Obviously, you want to brake as late as possible while
| still reaching the minimum speed demanded by the radius
| of the turn and your tires/downforce, which keeps your
| average speed as high as possible before the turn. But it
| very easy to get in a habit of braking too late,
| overshooting the turn, and taking a sub-optimal
| trajectory, which would be passed by someone who braked
| sooner and used some additional physics concepts.
|
| The absolute fastest way is to brake as late as possible
| without overshooting, start the turn while you are about
| to let off the brakes (when the weight of the car has
| shifted towards the front wheels while braking, so you
| get more grip on your tires which are doing the
| steering), and as you let off the brakes, the car has
| rotational inertia that carries through the turn without
| needing the tires as much. (but too much rotational
| inertia = spinout.) Once you have the rotational inertia,
| you can start giving it gas before you finish the turn,
| and if the car is RWD, use the engine/oversteer to both
| increase your speed again and give you extra force
| pushing you through the inside of the turn. (By getting
| slightly too much inertia at the start of the turn (but
| not enough to spin out), then at the end of the turn,
| when your car would go off the outside of the track,
| instead have it slightly over-rotate the turn, so that
| you can use the engine to angle your forces both forward
| and into the turn, to help you finish without going off.)
| This way you get to use the engine to make some of the
| turn instead of the brakes for all of it, which is
| obviously faster. Then straighten the wheel when you've
| exited.
|
| Drifting is just over-playing into the above mechanics,
| getting too much inertia too soon and doing a sideways
| burnout while countersteering (to bleed off the excess
| rotation) through the turn to look cool. The fastest is
| halfway between drifting and "driving naive", aka braking
| early and coasting through like normal road driving.
|
| I play racing sims and couldn't win consistently until I
| understood all the above.
| Filligree wrote:
| As sibling says, a proton moving through empty space
| would emit no gravitational waves.
|
| The galaxy isn't empty, however. The proton would be
| orbiting, emitting such waves, and yes, would slow down.
| jahnu wrote:
| Yeah that's why I mentioned a galaxy. Thanks, all!
| marcosdumay wrote:
| How would we do that?
|
| We will probably just keep downgrading its probability into
| more and more absurdly low values.
| api wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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.
| api wrote:
| It would be quite different from Earth in lots of ways.
|
| The most habitable region would probably be the twilight
| zone but "life will find a way" as Jeff Goldblum famously
| said. Life would have been evolving for billions of years
| in that environment before intelligence arose.
|
| The temperature gradient might not be as nuts as you'd
| think. A thick atmosphere would develop powerful
| prevailing currents that would move heat from the hot
| side to the cold one, basically a heat engine. It would
| keep the hot side from being insane and the cold side
| from being cryogenic. My guess is that the far poles
| would be extreme but anywhere from 1/3 to 2/3 of the non-
| twilight sides would be potentially habitable by
| something.
|
| If there were large oceans you'd get prevailing currents
| there that would move heat too.
|
| There'd also be a water cycle. Imagine regions of the hot
| side where it rains a lot. You might have this hot steamy
| jungle in eternal daylight, meaning 2X the energy
| available for photosynthesis.
|
| There'd probably be critters that would migrate around. I
| can imagine stuff living on the night side by eating
| those, scavenging, etc.
|
| I wonder if an environment with massive prevailing winds
| would drive the evolution of wind energy harvesting?
| Imagine a big tree like thing with big leaves or vanes
| shaped to flap in the wind and specialized cells that use
| that mechanical energy to make food and nutrients.
| Muscles go from sugars to motion. Seems plausible that
| something could go the other way, especially with
| billions of years of evolution and a massive amount of
| energy available that way.
|
| If that kind of thing evolved you could have wind powered
| ecosystems on the night side and solar powered ones on
| the day side.
|
| Lots of possibilities.
| chasil wrote:
| With continental drift, the moving land might regularly
| undergo sterilization events.
| jamiek88 wrote:
| Tectonics would be very unlikely.
| pfdietz wrote:
| Although rockets could take you between closely spaced
| planets, the delta V to escape the system would be much
| greater than in our solar system, by an order of magnitude.
| The habitable planet would be much deeper in the star's
| gravity well than we are in our Sun's.
|
| Travel times between inner planets would be very short, I
| admit.
| tomrod wrote:
| You should be able to sling shot multiple times to improve
| that though?
| pfdietz wrote:
| Some, although I think that would need either lots of
| slingshots or really heavy planets. If there are many
| closely spaced planets it could work, I think, and the
| encounter cadence would be high.
|
| If there are lots of planets in closely spaced orbits I'd
| think orbital resonances could force planets into
| elliptical orbits, which would drive strong tidal
| heating, as on Io (but more so, due to the much stronger
| gravity of the primary.)
| forgetfreeman wrote:
| Upvoted for "they probably look like crabs". I see what you
| did there and I am here for it.
| russdill wrote:
| If it's super easy to get to orbit, it's also super easy for
| your atmosphere to get to orbit.
| api wrote:
| True. I was thinking of time between planets though. It's
| hard to get to Earth orbit but it also takes six to twelve
| months to get to Mars without some kind of crazy torch
| rocket. In a smaller system it might take a few weeks. Big
| difference.
| jajko wrote:
| 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?
| 082349872349872 wrote:
| compare Forward, _Dragon 's Egg_ (1980)
| cheela wrote:
| For reference, https://mdpub.github.io/cheela
| 082349872349872 wrote:
| while we're at it*, RLF82: "Flattening spacetime near the
| Earth": https://journals.aps.org/prd/abstract/10.1103/PhysRev
| D.26.73...
|
| * (and I am admiring the _specificity_ of that HN acct)
| thechao wrote:
| Or, more directly, Niven's "The Smoke Ring" about humans living
| directly in an oxygenated accretion disk around a white dwarf.
| pfdietz wrote:
| The orbital speed of such a planet would be extreme, something
| like 300 km/s.
|
| This also means other planets (like Venus or Mars are to Earth)
| would be visible in the sky as perceptible disks.
| perihelions wrote:
| It's the same scale as the orbits of the large moons of Jupiter
| (roughly 0.003 au-0.013 au). If you were standing on one of
| those, the others would appear as very large disks--some of
| them larger than the Earth moon.
|
| (Jupiter itself would be much larger still).
| btilly wrote:
| 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.
| aw1621107 wrote:
| > 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.
|
| Isn't this a current limitation of our exoplanetary detection
| capabilities rather than something we know about other star
| systems in general? IIRC exoplanets are most easily discovered
| by the effect they have on their parent star's brightness when
| transiting it and/or due to causing the parent star to
| "wobble". Both those methods would tend to favor finding close
| and massive planets without necessarily ruling out smaller/more
| distant ones.
|
| Have exoplanet detection methods improved since I last read
| about them?
| Anarch157a wrote:
| A large enough telescope in space, with a coronagraph could,
| in teory, find such planets by direct imaging. Right now, I
| believe only JWST fits the bill, but using it for this
| purpose would interfere with other types of research, so the
| coronagraph us used only only to observe planets the wer
| already discovered by other methods.
| cruffle_duffle wrote:
| I'm pretty sure that new telescope being constructed in
| Chile will be large enough to directly image planets but I
| could be wrong.
| cruffle_duffle wrote:
| > Both those methods would tend to favor finding close and
| massive planets without necessarily ruling out smaller/more
| distant ones.
|
| They also favor ones whose orbit passes between us and their
| star, which dims the star and lets us see it. If the planet's
| orbit doesn't block the star, we'll never know it was there
| using our current toolset.
|
| I read somewhere that only like 2% of all planet's have
| orbits that come between us and their star--which seems like
| a plausible figure to me, it's a number you can probably
| derive from some simple math. This means until we find other
| ways to observe planets, we are only able to see a very small
| number of them out there.
|
| Incidentally if other intelligent life is out there planet
| hunting using the same method of observing planets pass
| between the star and the observer, it means the odds of them
| finding earth are pretty small. They'd have to be positioned
| such that the earth comes between our sun and their line of
| sight.
| bookofjoe wrote:
| "Dragon's Egg" by Robert L. Forward, published in 1980, is a hard
| sci-fi novel about intelligent life forms living on a neutron
| star. It's superb.
| FredPret wrote:
| That book is wonderful
| rokkamokka wrote:
| One of my favorite hard sci-fi books! Well worth a read
| danielbln wrote:
| Does it still hold up, technology prediction wise?
| Sharlin wrote:
| It doesn't really concern itself with human technology.
| Yes, there are humans, and a human spaceship, but their
| role is secondary at best.
| jamiek88 wrote:
| it's not really that kind of book. It's more physics than
| tech.
|
| Highly recommend to a certain type of person. Many of whom
| frequent this message board !
| mrangle wrote:
| 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.
| iamgopal wrote:
| While your argument is true, I would guess aliens will be quite
| a lot different than anything we know on this earth. Even
| different in so called life and death cycles, or even in the
| very definition of what we can call alive and dead. We should
| much broaden our search scope.
| devmap wrote:
| Depends how big his cory is
| jmclnx wrote:
| Nice read! FWIW, I built a system the other day, its name,
| "whitedwf" :)
| idunnoman1222 wrote:
| The end stage of stellar evolution cannot have life around it.
| There's not enough water beyond the frost line to renew any
| planet around a white dwarf.
| credit_guy wrote:
| Here's a (not completely flippant) answer: yes. At least in the
| case of Sirius B, and let's be hones, this is the case we care
| about, a planet that orbits it would be very close to Sirius A
| too. The distance between Sirius A and Sirius B is always between
| about 8 AU and 32 AU (1 AU = Sun-Earth distance). Since Sirius A
| is about 25 times more luminous than the Sun and Sirius B about
| 50 times dimmer, it is very likely that a planet orbiting Sirius
| B will receive most of its light/heat from Sirius A, and it would
| be somewhat comparable to what the Earth and Mars receive from
| the Sun.
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