[HN Gopher] Interstellar Mission to a Black Hole
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Interstellar Mission to a Black Hole
Author : JPLeRouzic
Score : 115 points
Date : 2025-10-24 09:17 UTC (13 hours ago)
(HTM) web link (www.centauri-dreams.org)
(TXT) w3m dump (www.centauri-dreams.org)
| api wrote:
| What's be super cool is discovering a! asteroid mass primordial
| black hole in our solar system. No epic interstellar flight
| needed.
|
| It would be super hard to detect though. We'd have to spot it by
| gravitational effects or get very lucky and notice lensing. It
| would emit nothing unless it happened to be nomming on some
| matter, and even then it'd be so small that the signal would be
| weak.
| noam_k wrote:
| That would be cool.
|
| I read somewhere that a black hole with the mass of the moon
| will absorb about as much cosmic radiation as it emits Hawking
| radiation. This is a fine line between "the black hole
| disappears before we can examine it" and "oops, we got eaten by
| a black hole".
| MomsAVoxell wrote:
| Hey, its not like an analog of "Yeah, lets just throw some
| more mass at the newly-forming black hole in our
| neighbourhood", said every human that has ever thrown things
| into the fire, forever ..
| gus_massa wrote:
| Sorry, but I have to link the " _Hole Lotta Trouble_ "
| episode of Pocoyo
| https://www.youtube.com/watch?v=HL_0OL7vZ44
| MomsAVoxell wrote:
| Yes, you really do.
| api wrote:
| Black holes aren't cosmic vacuum cleaners. They're just
| super super super compact objects.
|
| I've actually posted this a few times:
|
| If you suddenly transformed the Moon into a black hole of
| the same mass, it would continue to orbit the Earth in the
| same spot. It wouldn't suck up the Earth or anything. The
| ocean tides would continue as normal under the influence of
| the black-hole-moon's gravity, which would be the same if
| it was orbiting at the same distance. You wouldn't see a
| moon in the sky, but if you focused a good telescope on
| where it was you'd see gravitational lensing. It would be a
| little smaller than a BB.
| antonvs wrote:
| If it's in a stable orbit in the solar system, it wouldn't be
| able to "eat" us. Black holes gravitate exactly the same as
| any other mass, so it would have the same gravitational
| effect on Earth as any object if the same mass.
|
| What makes black holes special is that you can get much close
| to their center of mass than you can with normal objects.
| When you're that close - inside the radius that a normal
| density object of that mass would have - then you experience
| gravity at a much higher strength than normal.
|
| Put another way, even if our Moon was a black hole with the
| same mass, very little would change except that it would no
| longer reflect sunlight. Ocean tides on Earth would remain
| the same. You wouldn't want to try to land on it though...
| akomtu wrote:
| There was a movie where Moon was a hi-tech 'megastructure'
| with a white dwarf inside. I wonder if it would be
| theoretically possible to set up such a mini-dyson sphere
| around a mini-blackhole.
| api wrote:
| If you set it up at the right radius it would have 1g
| gravity at the surface, like a little mini-world. It
| wouldn't be able to hold an atmosphere though, so it
| would have to have pressurized buildings on it.
| the8472 wrote:
| We do not what such a thing anywhere near Earth though.
| https://arxiv.org/abs/astro-ph/9911309
| api wrote:
| Only if it evaporates, which it probably wouldn't do for
| billions of years.
| NL807 wrote:
| >It would be super hard to detect though.
|
| Would it? I would've thought there is enough dust in the solar
| system that it would create constant xray emissions. Even if
| it's faint, it would stick out like a sore thumb on super
| sensitive xray telescopes.
| TheOtherHobbes wrote:
| An asteroid-mass black hole is around a micron across. It's
| not going to be nomming on much because the matter
| distribution inside the solar system isn't that dense.
|
| Any tiny black hole born in the big bang would either have
| evaporated (if Hawking was right...) or would have grown much
| larger by now.
|
| Even a moon-mass black hole (0.1mm) wouldn't be eating much,
| although its gravitational effects would be much more
| obvious.
| antonvs wrote:
| We wouldn't have to get lucky if it was on the last stages of
| evaporating. If it has reached a mass of about a billion kg it
| would be shining plenty bright to detect, and would only have a
| few thousand years to live before destroying most life on Earth
| with gamma radiation.
| terminalshort wrote:
| According to this calculator
| https://www.vttoth.com/CMS/physics-notes/311-hawking-
| radiati..., the luminosity would only exceed that of the sun
| for 46.7 nanoseconds, so unless it's much less than 1 AU away
| we would probably be fine.
| terminalshort wrote:
| Could you find it by Hawking radiation?
| pavel_lishin wrote:
| I remember reading somewhere that it's possible for such a
| black hole to get captured by an asteroid (or vice versa, I
| guess), and happily live inside a rock, slowly orbiting inside
| the asteroid, sucking up atoms here and there.
|
| It would be detectable as an asteroid that's twice as dense as
| it should be.
| Cthulhu_ wrote:
| If it was asteroid mass, wouldn't it have the same
| gravitational effect of an asteroid itself? Plus, someone else
| mentioned it'd be like a micron across, which if my pop-sci
| understanding of these things is correct, it'd disappear in a
| poof of hawking radiation.
| api wrote:
| It would have the same mass, and it would be tiny -- like the
| size of a hydrogen or helium atom.
|
| AFAIK an asteroid mass black hole wouldn't evaporate _yet_
| since the CMB is still warmer than its Hawking temperature.
| Very tiny black holes would have evaporated earlier in the
| universe. A black hole evaporates when its Hawking
| temperature exceeds the ambient temperature.
| hansmayer wrote:
| Such a fantastic overview. And here we are, instead of building
| the infrastructure for accelerating solar sails, we're investing
| the money in AI-pornbots instead :/
| einrealist wrote:
| At least the AI-pornbots will operate from space. /s
| radu_floricica wrote:
| Considering AI-pornbots are increasing the derivate of the
| function, they might actually be the right move.
| TheOtherHobbes wrote:
| What are the odds the first alien probe to visit the solar
| system will be a pornbot or some form of marketing droid?
| Cthulhu_ wrote:
| If you subscribe to the Futurama school of comedy, very high,
| lol.
| prerok wrote:
| https://xkcd.com/1642/
| Cthulhu_ wrote:
| AI porn sells, solar sails are a research project at best.
| There is no money to be made from space flight, only discovery,
| and unfortunately capitalist forces far outweigh curiosity.
|
| Even the space race wasn't for science but for politically one-
| upping the others, doubly so because being able to bring a
| payload into space also demonstrates they can bring a payload
| anywhere on the world.
| Mistletoe wrote:
| How do you stop if your solar sail has you going near light
| speed? Or does it strand you halfway between stars in the
| doldrums where the force on both sides of your sail equals out
| from two stars?
| hvb2 wrote:
| You would fold the sail?
| voidUpdate wrote:
| That only stops you accelerating, it doesn't put the brakes
| on
| jordanb wrote:
| Deceleration is the same as acceleration. You use the light
| of the star you're approaching to slow down.
| Cthulhu_ wrote:
| But if you're going near light speed, the light /
| particles would be too faint to have any significant
| effect until you get very close. You'd basically just fly
| backwards straight into it. Unless your sail is very
| large and/or the total mass is very small.
| hansmayer wrote:
| That would not stop the probe from continuing to glide
| further. He's making a good point here.
| ceejayoz wrote:
| Gliding is fine. We whizzed past Pluto with New Horizons.
| Never stopped, just a photo flyby.
| SiempreViernes wrote:
| You don't stop this type of craft, it's strictly accelerate and
| coast type of thing.
|
| Also note that "solar sail" is a bit misleading, the (now
| apparently dead) Breakthrough Starshot design was a big
| reflector "sail" in space and _very many lasers_ on Earth to
| power it, it 's not actually driven by a stellar wind directly.
| zelos wrote:
| This suggests ejecting a secondary mirror in front of the
| craft to reflect light to brake the original craft:
| https://arxiv.org/pdf/1604.01356:
|
| _"...or by ejecting a reflector that is then used as a
| braking system (similar to thrust reversal on jets) but this
| only works if the payload is still within illumination range
| of the primary laser system "_
| dotnet00 wrote:
| Flipping the sail around would probably be the lightest
| option, though tricky because the larger sail designs would
| not be rigid.
| ianburrell wrote:
| Solar sails aren't powered by solar wind but by light
| reflecting off like the probe. But the probe would be powered
| by laser so not really "solar" sail. Light sail is the
| generic term.
| Razengan wrote:
| > _Or does it strand you halfway between stars in the doldrums
| where the force on both sides of your sail equals out from two
| stars?_
|
| This is actually I "love" to think about:
|
| What would it be like, to be "stranded" in the space far from
| any stars?
|
| or in the "voids" where there are relatively very few
| stars/galaxies to begin with?
|
| There _must_ be things drifting there right now...
|
| It would also be the perfect place to HIDE something :)
| jiggawatts wrote:
| If intelligent life evolved on a planet of a brown dwarf -- a
| "failed" star -- that was ejected from its original galaxy
| deep into intergalactic space, then that species would be
| spectacularly isolated.
|
| Note that the "naked eye" stars we see in our night sky are
| all big, bright stars in our immediate vicinity.
|
| Outside of a galaxy the night sky would be black, other than
| some fuzzy smudges of other galaxies.
|
| It would be a long time before any such species would figure
| out what galaxies are, what stars are, and their own
| relationship to those things.
|
| Their study of astronomy would take a wildly different path
| even assuming they end up at the same conclusions!
|
| And then what? What missions could they envisage, tens of
| thousands of light years away from the next nearest...
| _anything?_
| floxy wrote:
| Do we have a good estimate for the density of intergalactic
| stars? Or how far away from a star will you be on average,
| when you are, say halfway between the Milky Way and
| Andromeda?
|
| https://en.wikipedia.org/wiki/Intergalactic_star
| Razengan wrote:
| > _If intelligent life evolved on a planet of a brown dwarf
| -- a "failed" star -- that was ejected from its original
| galaxy deep into intergalactic space, then that species
| would be spectacularly isolated._
|
| Even better, (or worse): A species that evolved on a rogue
| planet! Without any star!! (heated by it's core or nuclear
| elements or space magic or whatever)
|
| > _It would be a long time before any such species would
| figure out what galaxies are, what stars are, and their own
| relationship to those things._
|
| Humans are bad enough with our "We're unique and special!"
| complex, imagine theirs!! lol
| dumpsterdiver wrote:
| It's where the future hides :)
| kakacik wrote:
| I don't think we can just go near speed of light. Even hard
| vacuum out there contains particles. Heliosphere is chock full
| of them, then Oort cloud has stuff way bigger than that (or any
| probe), even if sparsely spread out. Then there is cosmic stuff
| outside, as Voyager found out.
|
| Getting hit by some random molecule when orbiting Earth or just
| travelling say 30,000 kmh is one thing. Getting hit by swarms
| of molecules with say 0.5c can be catastrophic to the material.
| Now imagine wading through some space dust cloud, or even
| plasma cloud (ie remnant of some bygone supernova).
|
| Star trek had shields, and for good reasons. Super strong
| magnetic field may divert some charged particle, but helium
| molecule is just a helium molecule, no extra charge to play
| with.
| prerok wrote:
| Nit: shields were just for battle, for this they used the
| deflector.
| wartywhoa23 wrote:
| It is stated multiple times across the article that the probe
| would need a means of changing is trajectory, but not even a hint
| of idea how that could possibly be done is given. So the most
| important and blocking aspect of the mission is simply skimmed
| over, and the rest of it is built upon this omission as if it was
| something trivial to come up with.
|
| Does anyone have an idea how to equip a 1g spacecraft with any
| means to steer itself at 1/3 speed of light? The kinetic energy
| at that speed would seem to require something very incompatible
| with the weight constraint, to my understanding.
| antonvs wrote:
| Easy fix: change the description to "Interstellar Mission to
| the General Galactic Vicinity of a Black Hole"
| dvh wrote:
| Simply. You do Monte Carlo with the probes. You fire 1000 and
| one or two will have perfect trajectory so that no correction
| is needed.
| magnat wrote:
| Did you, by any chance, play Outer Wilds recently?
| gus_massa wrote:
| I don't think 1000, or even 1000000 are enough if you use
| random directions. Space is <huge>huge</huge>. This has been
| posted here afew times https://joshworth.com/dev/pixelspace/p
| ixelspace_solarsystem....
| estimator7292 wrote:
| Solar sails. You can fire a shit ton of lasers from the planet
| (or orbit) at the probes and very,very slowly boost them up to
| the desired velocity.
| marcellus23 wrote:
| It's not skimmed over, they cover it near the end in the
| "Requirements and challenges" section:
|
| > The most challenging phase of the mission may be related to
| how the nanocraft can transfer from an unbound to a bound orbit
| and start orbiting around the compact object. All possible
| solutions should be considered carefully. In the case the
| transfer is not possible, we may redesign the mission to
| perform the scientific tests when the nanocraft passes close to
| the black hole. For example, when the nanocraft is close to the
| black hole, it may separate into a mother-nanocraft (with a
| wafer and sail) and a number of small nanocrafts (without
| sails). The nanocrafts could communicate with each other by
| exchanging electromagnetic signals. The mother-nanocraft could
| compare the trajectories of the small nanocrafts to those
| expected in a Kerr spacetime and send the data to Earth.
|
| Light sales can theoretically be used to not only accelerate
| away from Earth, but also decelerate at the end of an
| interstellar journey (see Robert L Forward's work). The
| practicality of that is another matter.
| hinkley wrote:
| There's a really straightforward way to avoid a parabolic
| trajectory with a black hole. But data retrieval gets a bit
| difficult.
|
| More seriously, it floors me how often and consistently
| people forget that the accretion disk is essentially a
| partial accelerator and crossing or entering it will probably
| pulverize you to radioactive dust. Possibly before you could
| hit the event horizon.
| marcellus23 wrote:
| Not every black hole has an accretion disk, especially not
| isolated ones.
| sigmoid10 wrote:
| People don't realise this, but you can steer perfectly fine
| with a solar sail. That's because photons transfer momentum not
| just when they hit the sail, but also when they are emitted
| after reflection. So just by turning the sail at an angle, you
| can create a force in any direction perpendicular to the
| velocity vector. Using a two sail system, you can even
| accelerate and slow down along a single beam path. So you could
| theoretically travel to mars with a constant
| acceleration/deceleration phase (like a flip-and-burn in the
| Expanse) using only one beam emitter on earth.
| kragen wrote:
| How long would it take for a person to get to Mars with a
| sail powered by an Earth-based laser?
| lazide wrote:
| Infinite time since we have no realistic way of making such
| a laser at this time - and anyone trying it is likely to
| get nuked before they finish their massive death ray.
| palmotea wrote:
| > It is stated multiple times across the article...
|
| I was a bit confused by your comment, but I think the article
| you're referring to is not the OP, but the article the OP was
| commenting on:
| https://www.cell.com/iscience/fulltext/S2589-0042(25)01403-8...
|
| > Does anyone have an idea how to equip a 1g spacecraft with
| any means to steer itself at 1/3 speed of light? The kinetic
| energy at that speed would seem to require something very
| incompatible with the weight constraint, to my understanding.
|
| I'm also wondering how such a thing is supposed to communicate
| back to us over dozens of light years. That also seems
| incompatible with the weight constraint.
| NoMoreNicksLeft wrote:
| >I'm also wondering how such a thing is supposed to
| communicate back to us over dozens of light years.
|
| Split particle pairs. We just need to repeal the no cloning
| theorem, maybe if we promise to not use it for FTL
| communication the legislators would go for it.
| floxy wrote:
| >I'm also wondering how such a thing is supposed to
| communicate back to us over dozens of light years.
|
| Just spit-balling here. Send out the first batch of probes
| and then 5 years later send another batch of probes. The
| first batch of probes does their surveying for 5 years, when
| the later batch of probes start arriving. The data is
| uploaded to the late-comers, who aren't on an intercept
| course. Instead they are on a trajectory that causes them to
| swing around the black hole, and head on back to earth with
| the data.
| palmotea wrote:
| > Send out the first batch of probes and then 5 years later
| send another batch of probes.
|
| What's the separation there, at 0.33 lightspeed? 1.65 light
| years? Wikipedia says Voyager is 168.35 AU away, and Google
| says that's 0.00266 light years. Voyager has 23-watt radio
| focused by a 3.7m dish and its signals are received by a
| 70-meter dish on Earth.
|
| So you're talking about a 1g spacecraft signaling another
| 1g spacecraft over 620 times the distance to Voyager,
| without any of the beefy equipment that exists on both ends
| of the Voyager link.
| floxy wrote:
| Hmm. Seems like you are you multiplying 5 years by 33% of
| light speed to come up with 1.65 light years? I
| apparently didn't explain well enough. The 5 years is for
| the first batch of probes to gather data over an extended
| period of time (while in orbit around the black hole).
| The second set of probes is just a roundtrip "fly-by" to
| collect the data from the first probes and return it to
| earth. No reason that the return trip probes would have
| to be very far from the data gathering probes. Maybe you
| can't orbit close enough to the black hole at these
| speeds without getting too close to the accretion disk?
| palmotea wrote:
| Even then, I think you're going to have massive distances
| between tiny probes moving very fast relative to each
| other. Maybe not 1.65 light years, but communication over
| Voyager's 0.00266 light years or even a much smaller
| distance (e.g. Earth to moon) seems insurmountable for
| two 1g probes.
|
| Also, the probes are in deep space, right? No solar
| power. Where are they going to get the energy?
| floxy wrote:
| https://en.wikipedia.org/wiki/Betavoltaic_device ?
| floxy wrote:
| So skip the communication, and just have the one probe do
| the gravity assist to get headed back to earth with the
| data it collected.
| floxy wrote:
| Since momentum is conserved, why not just have a 2 of the 1 g
| probes strapped to each other with a spring in between. When
| you need a course correction at 100 AU out (or whatever). The
| probes calculate how much of a correction is needed, adjusts a
| screw that tightens or loosens tension on the spring, reorients
| itself appropriately with a reaction wheel, then the two probes
| are released from each other, begin pushed apart with the
| spring. One probe gets the trajectory correction it needs, and
| the other gets further off course. Maybe with some gravity
| assists with nearby objects.
|
| https://en.wikipedia.org/wiki/Gravity_assist
|
| also:
|
| Roundtrip Interstellar Travel Using Laser-Pushed Lightsails
|
| https://ia800108.us.archive.org/view_archive.php?archive=/24...
| vjvjvjvjghv wrote:
| Isn't that basically how a rocket works? Throw stuff out one
| side to get the thing on the other side moving. Not sure how
| this would compare to a rocket engine with hyperbolic fuel.
| floxy wrote:
| Yes.
| dylan604 wrote:
| It compares in that it doesn't require said hyperbolic
| fuel. That fuel is heavy and finite.
| lazide wrote:
| Uh, it does - the 'fuel' is the other probe.
|
| Notably, this also has a particularly bad ISP?
|
| Also, probes are presumably also heavier and rarer?
| hinkley wrote:
| Only in the sense that throwing a knife at someone is the
| same as shooting a howitzer at them.
|
| Specific impulse.
| vjvjvjvjghv wrote:
| As far as impulse goes, the spring will probably be
| pretty inefficient relative to mass.
| hinkley wrote:
| The point we are trying to make is that there hardly
| anything that would be less efficient relative to mass.
| sandworm101 wrote:
| No. Very much no. The spring system would literally throw
| away half the mass of the craft for, maybe, a 10m/s
| delta. Fireworks would be more efficient. A pitching
| machine attached to a huge pile of baseballs would be
| more efficient (ie the baseballs could be thrown faster).
| hinkley wrote:
| Because the specific impulse of the spring is negligible when
| you're moving at 1/10c and why would they send a 1g probe if
| they could accelerate 100kg to that speed? Why do you suppose
| doubling the weight would be free instead of making the
| system infeasible?
| Alex-Programs wrote:
| That's just a really, really ineffective rocket. A spring has
| nowhere near the energy density of chemical fuel.
| Cthulhu_ wrote:
| What would the "screw" push off of? That rotational force
| would need to go somewhere or be corrected, else the probes
| would just rotate. I guess a gyroscope could do that, but
| what you're describing just sounds... very roundabout, and in
| terms of force, a few kilos of propellant would have the same
| effect.
| floxy wrote:
| This is infeasible for the reason other have mentioned
| about specific impulse. But surely you can imagine a set of
| parallel boards with a coil spring between them and a set
| of cylindrical guide rods to prevent relative rotation
| between the boards. A motor fixed to one board turns a
| screw that engages with threaded nut on the other board,
| mounted on a thrust bearing, and guide bushing that allows
| a linear movement, but disallows the rotation degree of
| freedom. Think of the lead screw on a milling machine or
| lathe.
| stronglikedan wrote:
| gyroscopes?
| bawolff wrote:
| > So the most important and blocking aspect of the mission
|
| Idk, i think the fact they are using statistical arguments that
| there should be a nearby black hole, but haven't actually found
| any or have any idea where they are, is pretty blocking.
| ithkuil wrote:
| "steering" is a word that can lead to confusion because it
| leverages the intuition that we have with our ground vehicles.
|
| A change in direction in space requires accelerating the
| vehicle in some direction, the effect of which is just simple
| vector addition of the velocity vector of the vehicle.
|
| So if you are going with a huge velocity in one direction and
| you want to change direction significantly in another direction
| you have to change velocity (accelerate) a lot in order for the
| combined vectors to produce a significantly different final
| velocity vector
| vee-kay wrote:
| Related: "Project Solar Sail" by Arthur-Clarke and others, is a
| good anthology (stories, essays and illustrations) about the new
| Age of Sailing (Sailing in Space)via lightships and solar sails.
| ck2 wrote:
| The most aggressive yet most realistic project we could
| reasonably do is the SGL Telescope
|
| Won't happen under this administration and really might take a
| planet-wide effort but it would be incredible
|
| https://www.centauri-dreams.org/2022/07/22/solar-gravitation...
|
| https://www.nasa.gov/general/direct-multipixel-imaging-and-s...
|
| https://www.universetoday.com/articles/a-mission-to-reach-th...
| amai wrote:
| What is the point of such a mission? There is literally nothing
| to see there.
| Cthulhu_ wrote:
| A black hole may be invisible but its accretion disk and the
| effects on the light being deflected around it are anything
| but.
| hunterpayne wrote:
| Isn't Relativistic time dilation a problem for this idea? To the
| probe, the trip is only a few centuries but to us on Earth,
| millions of years. Maybe 0.1c isn't enough to cause this to be a
| huge problem but I think it is. Perhaps one of you Einstein
| enjoyers can tell us for certain.
| kakacik wrote:
| No need to be snarky and especially not here re basic science.
| Time dilation happens exponentially, ie with 0.5c you don't
| have time going 1/2 slower, rather a miniscule amount. Once you
| keep approaching speed of light closer and closer, all things
| go extreme (time, energy required, mass and so on).
| turtletontine wrote:
| Time dilation is 1/sqrt(1 - (v/c)^2). So at 0.1c that's 0.5%.
| Certainly much higher than any human has ever experienced! But
| not exactly gonna change 100y to 100,000,000y.
| prerok wrote:
| Time dilation is exponential. At 0.1c it's definitely
| measureable but not a practical problem.
| optimalsolver wrote:
| Having read Michael Crichton's Sphere, I think I know how this
| ends.
| LogicFailsMe wrote:
| Seems like first we need to get out of the gravity well... Then
| we need to cure ageing to give people skin in these games... Then
| we need to crack FTL or find a way to cryo-sleep or we end up
| with dystopian science fiction ships of the damned...
|
| Not in my lifetime I suspect...
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(page generated 2025-10-24 23:00 UTC)