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So, assume that there's a superstructure roughly the size of Pluto (~1,475 miles in diameter is the figure I found) that an organization doesn't want to be easy to find. Hiding it in the void between solar systems in an out-of-the-way corner of the galaxy seems like an effective way to do so, given the sheer amount of distance involved. It is supremely unlikely that someone would just stumble across it- it would take reality-breaking levels of luck for them to just happen to pass within visual range- and this seems like an effective measure against discovery.
The only problem I can foresee is scanning technology. What would be an effective way of preventing scanners from picking up the superstructure? Or, at the very least, disguise it so that it appears to be something else that nobody would bother taking a closer look at?

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    $\begingroup$ When it comes to space, "visual range" can encompass up to the entire galaxy (depending on luminosity, obscuring nebulae, and telescopic resolution). $\endgroup$ – cowlinator Sep 2 at 21:15
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    $\begingroup$ "Scanning technology" is pretty vague. What level of technology are we dealing with? Is the technology level of the people who are scanning equal to the technology level of the people who created the superstructure? $\endgroup$ – cowlinator Sep 2 at 21:17
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    $\begingroup$ Also, how long does it need to stay hidden for? 100 years? 100 million years? $\endgroup$ – cowlinator Sep 2 at 21:46
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    $\begingroup$ What does that structure do? This is really important, in order to understand how much heat it dissipates and how bright it shines in infrared. $\endgroup$ – AlexP Sep 2 at 21:52
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    $\begingroup$ VTC:Needs Details. (a) How far away is this space station from the closes inhabited system that could do something about it if it were detected? Information cannot travel faster than the speed of light. So if said object were 1,000 LY from Earth, the earliest we could detect it would be 1,000 years later even if it glowed white hot. (b) Agreeing with @cowlinator, how long must it remain hidden (speed of light....)? (c) what and how much energy is it producing, if any? (A dark object would be next to impossible to detect from any random direction.) (*continued*) $\endgroup$ – JBH Sep 3 at 3:15

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Really, really, really difficult.

Space is just that big. To give you an idea of how big space is, in the science fiction novel The Stars, Like Dust, one of the plot points is that they're seeking a (supposedly unmapped) star system which was found by a random jump within a nebula. One of the characters points out that the odds of jumping correctly to any star system was one 1/250,000,000,000,000,000. And that was an entire star system within a nebula and star systems are huge, dozens of orders of magnitude larger than Pluto and you're hiding this in an entire galaxy. The effective way of hiding it is generating a sufficiently random method of obtaining a set of blank space to put the space station in, and hide there. You will simply not be found, no matter how hard the enemy looks, unless they have access to literally quintillions of space ships all seeking you out.

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    $\begingroup$ @cowlinator The jump was executed completely randomly without a fixed endpoint in mind, so the ship could have showed up anywhere within the nebula and it (somehow) would up next to a star. $\endgroup$ – Halfthawed Sep 2 at 21:46
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    $\begingroup$ I see... so the probability includes all of the empty space outside of any star system $\endgroup$ – cowlinator Sep 2 at 21:48
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    $\begingroup$ Having cleared that up, I don't think the odds of it existing at any particular location are deeply related to the odds of finding it. Anything that has mass exerts a gravitational pull, and that will effect the paths of brightly luminescent things like stars. We can even find gas and dust this way. $\endgroup$ – cowlinator Sep 2 at 21:59
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    $\begingroup$ True. But that information is limited by the speed of light which means that it will take a long time for that information to get anywhere, and even when it does, moving your base every year or so via random jump neatly solves that problem. $\endgroup$ – Halfthawed Sep 2 at 22:05
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    $\begingroup$ It's unclear what a "jump" is, and whether it's possible in the questioner's universe. $\endgroup$ – cowlinator Sep 2 at 22:15
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Hiding it in the void between solar systems in an out-of-the-way corner of the galaxy seems like an effective way to do so

It is, if you have potential access to all of those star neighbourhoods.

Scanning the immediate neighbourhood of any given star is not too difficult, lengthy, or expensive. And your superstructure will radiate some heat due to simple thermodynamics. In interstellar space I would expect nothing to radiate above the cosmic background, and doing "milk runs" to a suitably also hidden solar system to resupply large quantities of frozen helium to act as a thermal sump would be really expensive.

Using FTL, scanning is made even easier because it allows you to look "back" in time: by making ten FTL jumps, one light-year apart, towards a likely zone, you get to see how it was for the last ten years (so, you need to guard not only against the current superstructure emission, but also against its, probably much larger, emission during construction and before baffles and stealth systems were installed. That emission is expanding throughout the galaxy at the speed of light, and can be detected and traced back).

But the stars are really many, so if you don't know which is the star the superstructure is nearest to, the need to run the "simple, fast and cheap scan" around all possible stars quickly balloons into a difficult, slow and horribly expensive endeavour. Mission accomplished.

A further possibility is to hide not too far from a very noisy system, that makes scans difficult. Provided that there are a lot of them, so the possibility of an extra deep scan near noisy systems avails nought: you don't want to be in the last place someone would look, because that is the first place where someone cleverer would look.

Something I would definitely do is disseminate decoys. Generating a small quantity of heat and radio disturbances is easy and cheap, so preparing a thousand decoys would be no great trouble. You find a trans-neptunian object that might be your superstructure, you plant inside a radio noise transmitter with random activation scheme. Then, whoever stumbles by will have to run extra scans to investigate, which will both make them lose valuable time and resources in striving to find something that isn't there, and warn you that a search is under way and what resources it may have (if you get one decoy hit per year, or two per years in the same area, or several all over the galaxy, it changes things).

Also, you want to built and distribute the decoys from some place at a random distance from the superstructure (i.e., anywhere else in the galaxy), so if anyone has the resources to thoroughly analyze the decoys and their placement, they will converge on the decoy's source, not on the superstructure.

More on decoys

As @Bohemian noted, you don't want the decoys to look like decoys. You would set up something that has a plausible reason of being, and just happens to duplicate the emissions from your stealthed superstructure.

For example, you get a cold trans-neptunian object and install a suitably powered WiFi mesh on its surface. The mesh connects sensors around cheap carbon crystals covered in lead, and all it does is report continuously "Device operating properly. Nothing to report" packets. Should someone find the network...

"We have analyzed the structure, Captain. It is a blend of some very simple and a little bit of very advanced technology, but very logical."

"Explain."

"There are some three thousand spheres all over the planet, apparently deployed from orbit. They are wirelessly linked, and it is their emissions that we detected. Each sphere is radiation-shielded and encloses a crude event detector not unlike those in use on Earth in the Twentieth Century. They are all connected with an advanced relay buried near the North Pole."

"So if one of them detects anything...?"

"Exactly, Captain. A very sophisticated medium-range omni-directional subspace transmitter at the Pole triggers an alarm. The explosion we detected the day after tampering with one of the spheres was in all likelihood the real relay station, thirty light-hours distant and running cold. It woke up, transmitted the true alert to its masters through means unknown, then self-destructed. The Pole central clearly misunderstood our tampering for whatever event it was designed to detect, and sent the alarm."

"But what should have normally caused such an alarm? What are those sensors for?"

"Unknown, Captain. Some extremely energetic event, some kind of subatomic particle perhaps, capable of bypassing the thick radiation shield, and yet interact with the carbon-silicon-aluminum matrix inside. Nothing known to Federation science could do this. The matrix is cheap, but clearly carefully designed for this specific purpose. Unfortunately, the builders apparently did not take into account the possibility of someone tampering with the detector itself. But the Oort station self-destructed in an extremely energetic manner; what you would call a serious case of overkill. They wanted to be sure nothing could ever be recovered from it."

"A dead-drop alarm... whoever did this was scared. Really, really scared. Of what? Of whom?"

(some months later)

"We have found fifteen planetoids converted to sensors in this arm of the Galaxy alone, Captain. There probably are many others, scattered at random. All within two light-years from the nearest star. We're now just cataloguing them with long range scans to see whether their distribution yields any insight; landing for samples would be illogical, seeing as how they're all essentially identical."

"Their builders are, or were, hiding from an enemy in possession of some technology we don't even comprehend, and potentially appearing anywhere in this part of the Galaxy. The builders themselves are probably extinct, but..."

"The one they hid from may not be. We are considering deploying the same kind of sensors they employed; we don't understand how they could work, but the sensor matrix is easily duplicated and their operation is straightforward."

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    $\begingroup$ +1 for mentioning the idea of using FTL for looking backwards in time. Also at first I thought decoys would just make it more obvious that there was something to look for, but I would +1 again for the idea of using those decoys as detection/analysis/prediction of who is looking at/for your stuff. $\endgroup$ – mtraceur Sep 3 at 17:53
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    $\begingroup$ One additional concept on top of the decoys: If you have a high enough level of technology and resources, you can also make them look believably like real installations. Like small outposts for travel or research or supply caching or defense. Suddenly it turns out that ancient forerunner race isn't really gone at all, and in fact all those "abandoned" facilities we keep finding have been subtly "watching" us the whole time. Or, if you're willing to be known as an organization/government/species, keeping them manned lets you shape the narrative and learning from them when anyone finds them. $\endgroup$ – mtraceur Sep 3 at 18:01
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    $\begingroup$ The trouble with decoys is if the decoys are discovered to be artificial, it may tip an observer off that there's something they are a decoy for and bring more attention to the region. $\endgroup$ – Bohemian Sep 3 at 23:31
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    $\begingroup$ Any decoys anywhere hint at something hidden. $\endgroup$ – Bohemian Sep 4 at 9:31
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    $\begingroup$ +1 for the decoys making your opponent paranoid 😃. $\endgroup$ – Matthew Sep 4 at 15:20
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Hidden in plain sight:

There are lots of small planetoids floating around out there, and we are continuing to find more of them. This is pretty much what the Kuiper belt consists of. Most of them are cold, airless balls of rock with little to nothing to interest anyone. In your future universe, I'm assuming there's some sort of FTL system that allows travelers to reach such bodies if they desire. The key is to make people not desire.

Since there are so many airless balls of cold interstellar rock, let's assume those who want such things can find them. Hopefully, there is no real demand - unless you're sneaky, a slightly warm ball of rock near a star has way more going for it.

Given enough tech, an advanced civilization will be tracking all these things with telescopes and the like, but academically. There's no real motive to care. So pick one, preferably one that has been investigated and found completely boring, and claim it for Intergalactic Amalgamated Metals Inc (fictitious shell corporation). Build your superstructure inside the planetoid, or fake a planetoid (less desirable, since a magically appearing planetoid is interesting...)

Of course, Intergalactic Amalgamated Metals Inc goes belly up because the planetoid is so uninteresting, and "abandons" their mining operation. So now you have a reason for ships to have gone there, reason for structures (should anyone bother to scan them), Ownership of your worthless rock so you can discourage visitors, and justification for ships to visit (the new owners are inspecting the site).

The only risk is that people may be interested in an abandoned mine, so the records should show there is no reason to go - the owners blew it up so uninvited visitors couldn't sue them, or there's a (fill in the blank) hazard that makes it both pointless and dangerous to go there, like an industrial accident has made it radioactive.

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    $\begingroup$ "Khyber" belt? Do you mean Kuiper belt? $\endgroup$ – Nzall Sep 3 at 7:00
  • $\begingroup$ @Nzall Yes, thanks, darn spell check. $\endgroup$ – DWKraus Sep 3 at 11:58
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    $\begingroup$ Just be sure to put your radiators on the side away from the Sun, so infrared telescopes won't pick you up. $\endgroup$ – John Doty Sep 3 at 17:33
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    $\begingroup$ If you're doing anything with it, you'll need power, and you'll need to radiate that power away as heat after you've used it. You probably can't feed a human for less than one megawatt by the time you concatenate the inefficiencies of a heat engine making electricity making light illuminating plants to fix CO2 and only eating the edible bits. $\endgroup$ – John Doty Sep 3 at 23:57
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    $\begingroup$ The only problem I see is that Space is so big that by Amalgamated Metals Inc saying you don't want to go somewhere is a bigger claim to fame than saying nothing at all. Chernobyl for example got over 10,000 tourists last year, which is a lot more tourism than it got when it when is was a boring old place that wouldn't kill you. $\endgroup$ – Nosajimiki Sep 4 at 13:28
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It all depends on what you mean by "scanning technology."

Space is, as we all know, very very big. There are probably billions of rocks moving around and between the stars. Our models of planet system formation say they should be there, but we haven't actually seen them, which tells you something right there.

Most of these rocks are (supposedly) much smaller than Pluto, but they would still add enough noise that scanning would be very hard.

With today's scanning technology hiding would be trivial. The only reason we can see Pluto is because it is so close to us.

But who knows what future technology will bring? You know, because you are the author. You can decide both how future scanners work, and how future stealth technology works. As long as you are fairly consistent about it, nobody will complain.

Gravity

The one thing we cannot hide today, and we probably never will, is gravity. Even if we discover artificial gravity, Pluto is probably too big to hide. OR, it will use too much power.

With today's tech, we cannot see gravity directly, we can only see that other objects are moved by it. As long as you stay far away from everything, you are safe. Today.

Future tech might see gravity directly and more detailed. That would make another Pluto stand out from the much smaller rocks around it.

Unless it is hollow. You have told us how big the thing is, but not how heavy it is. The obvious defense against a gravity detector would making your object as light as possible. But that will also make it fragile, so there is a question of what is worst.

Power and heat

You haven't told us what this object is going to do. If it is just a storehouse it won't need power, but if it does something more active, it will use power. And that means it will radiate heat. If there are people on board, they will want to live and work in reasonably warm rooms.

Heat can be detected fairly easily, but space is still big. A rock glowing a little bit will only be detectable from relatively close by.

Of course, this will change. Detectors will be better in the future. How much better, only you know.

One can limit power usage and room temperature, but probably not very much.

There are likely to be trade-offs where they can hide from one type of detector, like gravity, but only by using power and glowing hotter.

One can, for a short while, let the heat build up and not escape. This is like holding your breath, not recommended for long periods.

More reasonable is controlling the directions heat escapes. Let refrigerated panels shield the object in directions you expect scanners to be, that is nearby stars and shipping lanes.

The downside of this is that the object will glow brighter in other directions. Refrigeration takes power, and power gives heat. If an enemy ship approached from an unexpected angle, they have lost.

Travel time

A supply ship departs for parts unknown. It returns two weeks later, empty. A reasonable assumption is that there is something one week travel time away.

That in itself is not very interesting, but if the enemy combine travel times from several different directions the possible locations shrink rapidly.

This will be fairly inaccurate, but it allows them to let their scanner ships concentrate on a much smaller region.

This will be a spy vs spy game. Obviously they aren't going to mark their supply ships "Secret Base Supply Ship", but the enemy can find out in other ways. Keep your secrets secret!

The enemy can be aided by massive computer analysis. This is likely to happen long after the fact, where they can infer the building of the object many years afterwards by going through old computer records.

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  • $\begingroup$ We can detect gravity, actually. That's how we know how much dark matter is concentrated where. We can observe the gravitational lensing caused by gravity. And there is nowhere in space you can hide this, other than hiding it in something that's already massive, because the cosmic background radiation is everywhere. And the problem with putting it somewhere there's already a lot of mass is, you want it far away from anything else. $\endgroup$ – Ton Day Sep 3 at 9:32
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It will be found pretty easily.

Technology evolves in leaps. The first time we suspected something was an exoplanet was in 1917. We got the first confirmation in 1992. On August 1, 2020 we knew of 4,301 exoplanets (it's all in this link). That's a huge leap in exoplanet detection - from 1 candidate to 1 confirmation in 75 years, then 4,300 new finds in 28 years. This year an AI scooping on old data from NASA found further 50 exoplanets.

Just the same - we know of a few objects that might be rogue planets, which is the class of object your structure would be. These are hard to detect, and the smaller they are the harder they are to pinpoint. In the past we could only detect things much larger than Jupiter, but three of the current candidates have sub-jovian masses. In a couple decades we might know of hundreds or thousands of these, and we'll be able to map their orbits around the galaxy.

If your organization has the technology to hide it in the interstellar void, then someone will have the means to find it. I can just imagine a bunch of nerds analyzing star orbits and going "hey, why is Proxima Centauri off its projected path for the next 10,000 years?"

Two scenes from Star Wars come to mind:

  1. When the protagonists of Rogue One hack into a database to obtain data about the Death Star;
  2. When Obi-Wan Kenobi is outsmarted by a child while trying to find a planet that is not in the stellar maps available to the Jedi Order.

OBI-WAN
This is where it ought to be... but it isn’t. Gravity is pulling all the stars in this area inward to this spot. There should be a star here... but there isn’t.

YODA
Most interesting. Gravity’s silhouette remains, but the star and all its planets have disappeared. How can this be?

There is a brief pause. Then a CHILD puts its hand up. YODA nods.

JEDI CHILD JACK
Because someone erased it from the archive memory.

CHILDREN
That’s right! Yes! That’s what happened! Someone erased it!

JEDI CHILD MAY
If the planet blew up, the gravity would go away.

OBI-WAN stares; YODA chuckles.

YODA
Truly wonderful, the mind of a child is. Uncluttered. To the centre of the pull of gravity go, and find your planet you will.

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    $\begingroup$ The gravitational effect of even a Jupiter-sized mass at one light-year on Sol would be negligible. At those levels, all stars will show errors in their projected paths, because there are a lot of rogue planets and opaque mass distributions that won't be charted. $\endgroup$ – LSerni Sep 3 at 16:08
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    $\begingroup$ This doesn't explain how to distinguish the installation from the other rogue planets. Easily finding all random asteroids and rogue planets doesn't mean you'll know which one is your target. $\endgroup$ – Erik Sep 4 at 9:12
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DWKraus's answer - Hidden in Plain Sight - is excellent.

I'm just going to develop that idea a bit further, in a way that's too long for a comment.

DWKraus' answer boils down to: don't hide it - show it, but as an either utterly boring or unattractive phenomenon. With several good ideas on how to do this. I'm going to focus on the boring, "can't be bothered" aspect, inspired by two authors.

  1. Douglas Adams (HitchHiker's Guide). Making anything invisible is incredibly hard. It's much easier to surround it with a Somebody Else's Problem (SEP) field. People observe the thing, but instantly turn away and forget about it.
  2. Iain Bank's idea of "interstitiality". In that novel Banks's protagonist is a member of a quirky cult, one of whose rules is that, when forced to enter the normal, "unclean" world, you must never do things in the usual way, but find a way to slip through the cracks between systems, customs, normal way of living. (The Hungarian concept of the kiskapú or "small [side] gate" is similar, but refers to getting things done in an overly bureaucratic state).

What I'm suggesting is to engineer the invisibility of your planetoid, but using social rather than technical engineering.

How, in the context of your world, might you encourage anyone who might be interested, who happens to stumble across evidence of your planetoid, to actively not want to investigate any further - to react not with curiosity but with indifference, or even with an active desire to do anything else (clean the bathroom, de-claw the cat)? In other words, how to create a real SEP field?

Perhaps the disguise this planetoid adopts, in official records, could connect it with a difficult, burning issue, which people would rather just not deal with. A recent traumatic war; a pandemic; some religious prohibition. Whatever impression your planetoid projects, it needs to be tiresome rather than challenging, evidently boring rather than noteworthy or enigmatic.

Or, using the idea of interstitiality: you disguise it (using an artificially-created emissions spectrum, for example) as one of millions of objects which fall between two jurisdictions. For example: according to Galactic Exploration Institute's records (which you have "improved" for your own purposes), this object is being surveyed by the Institute for Galactic Exploration; according to IGE's records, it's the GEI who are responsible for investigating it. Both the GEI and IGE are immensely bureaucratic, and they loathe each other.

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Hiding it is not a problem. Minimize all transmissions from it, make it as close to a black box object as possible, and burry it in random noise.

The provlem is, how do YOU know where it is? There is no GPS system for the galaxy. There is no galactic coordinate system. You can't put a dot on a star map and say 'there it is', because no star map is static. You know you put it somewhere, but where is it now?

If there is no way for the other side to detect it, there is no way for you to detect it.

As soon as you put some sort of tracking beam on it for your use, so you can find it, it is no longer invisible for the other side, either.

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    $\begingroup$ I am fairly certain that by the time we can build a Death Star in interstellar space, we can also navigate it. The stars are moving, but in predictable paths. $\endgroup$ – Stig Hemmer Sep 3 at 7:38
  • $\begingroup$ @Stig Hemmer Unless they have instantaneous travel, wormholes or whatever, 'predictable paths' just can not stand up to light taking hundreds of years to traverse void space.'I am sure I saw it here yesterday - wait, that was two centuries ago by light travel. Travel through a worm hole to pooint B, everything is different because now the light is either earlier or later than it was at point A. Star charts show how it USED to be. Showing it as it is NOW is useless - no one can see them 'now'. Look at me, I'm here, but I will be there when you see me now. Problem starting to clear up? $\endgroup$ – Justin Thyme the Second Sep 4 at 1:15
  • $\begingroup$ @JustinThymetheSecond But we'll be able to predict how things are different. If we know its motion relative to some larger body with a known position, we can always calculate how to meet up with it at whatever speed we're going. We can tell distance and speed, so even if we only know where it was 300 years ago, we can tell where it is now. $\endgroup$ – Redwolf Programs Sep 4 at 19:49
  • $\begingroup$ @ Redwolf Programs When is 'now'? Unless one posits instantaneous communications and travel, even though we can calculate where on object SHOULD be, 100 light years away, we are not there 'now', it will take a long time to get 'there'. No matter how advanced computing power gets, we will never get there. Just too many variables, too many unknowns, too many equations. That 'some larger body with a known position''s 'known position' is no longer valid. We no longer know where that 'large body' is. $\endgroup$ – Justin Thyme the Second Sep 5 at 13:21
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For humans - very hard, for computers, who create a 3d representation of disturbances- not so much.

You need two observatorys, that can capture all wavelengths, in all directions simultanously in hiRes and store it.

One can be near earth, the other- needs to be ahead or behind in flight direction of the solar system, best would be synced otherwise regarding orbits to earth.

From those two captures, a 3d model of all background oclusions to the neighbourhood could be computed. Apply physic predictions and orbital mechanics and you can map the void between the stars pretty good.

https://en.wikipedia.org/wiki/Parallax

You could even add some automated probes, that track "intersting occlussion object vectors" - something obscures a nearby star, you nudge a bunch of probes away from the observatory, tracking the one for which the object stays occluded the longest.

Loads of fun.

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  • $\begingroup$ And assumes instantaneous communications and instantaneous travel of those 'probes'. These monitoring stations would have to be everywhere in the galaxy, given that 'occluded light' coul dhappen anywhere in its one hundred thousand year journey through space.time. You would never know WHEN it was occluded. So many people just think 'space' when it is really 'space/time'. Think 'light-years/speed-of-light' for 'distance/time' and then realize that 'distance' is no longer valid over that 'time', the universe has expanded or even curved differently during the 'time' the light 'travelled'. $\endgroup$ – Justin Thyme the Second Sep 5 at 13:41
  • $\begingroup$ There is a certain 'time frame/time-period' point after which concepts of 'distance' become meaningless and no longer apply, because that 'distance' changed over that 'time'. Only if one considers instantaneous information transfer, instantaneous commuications, and instantaneous travel does really long (hundreds of light years) 'distance measurements' mean anything. $\endgroup$ – Justin Thyme the Second Sep 5 at 13:46
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Given that it can make FTL "jumps", all you have to do is move it every so often so that even if it is detected it is long gone by then.

As others have mentioned the radiation it gives off and gravitational pull it exerts are limited by the speed of light, so in order to detect it and then jump to its location it would have to be in the same place for at least as long as it takes light to travel from it to the nearest observer.

So then all you have to do is pick a random place that is at least one light year away from any possible detectors (preferably much further) and then have it move every six months or so just to be on the safe side. If jumps are expensive then have it hide even further from people and jump less often

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If the largest concern is detection via infrared radiation, then one possibility would be to hide closer to a (uninteresting, probably a red dwarf) star.

After all, if you need to emit enough radiation to heat your object to 50K, then if the other objects that you are mimicking are only 10K, then you'd stand out. However, if you were closer to a star, and so you should be at 300k, well, you being 340K would not be that exceptional.

And, with a bit more effort, you could take an advantage of variable albedo to further hide your heat signature. If we have an object with higher albedo towards the star (e.g. mostly white), and lower albedo away from it (e.g. mostly black), then it would be naturally cooler than if the albedo was evenly distributed (and this is not a violation of thermodynamics; it happens because the object is thermally more tightly coupled to the cold interstellar space than the hot star).

Now, if the object is rotating (and most natural objects will be), then this effect averages out over time. On the other hand, if we have an artificial object, we can deliberately change the albedo, for example, one low-tech way would be to expose white shutters when facing the star, and black shutters when facing away.

This results in a thermal deficit over a natural object; we can use the away-from-the-star side as a thermal dump (and if we dump the right amount at the right time, we'd generate the same heat distribution as a natural object).

To detect this from thermal anaylsis, the scanner would have to get close enough to see that the albedo of a specific spot on our planetoid changes over time; that is plausibly out of scope for a general galaxy-wide scan.

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Communications systems...

They csn hide in a bok globule, which is a solar mass dark cloud, perhaps more common than stars but uncountable currently because black against black backgrounds.

The hidden base would probably send and recieve communications and use energy, probably directional electromagnetic waves like light or radio of some wavelength.

Only energy that is emitted by the station energy systems or its communicatons can be detected by deflection from gravity or reflection by cloud or a panel of the station something.

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