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I have been wondering how galactic features could impact interstellar civilizations in the process of colonizing a galaxy (either andromeda or the milky way).

According to this video these features, specifically the arms and the core, could be areas in which life would have a harder time developing due to stellar activity and radiation, but I can't help but wonder if they'd also be obstacles for spacefaring and interstellar civilizations.

Additionally, the interstellar civilizations in my universe have access to FTL technology but it requires very precise calculations and conditions in order to be exploited not to mention that generally it can only be used to jump only to nearby systems due to energy constraints.

So with these considerations, would these features be relevant obstacles?

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  • $\begingroup$ What is the range of the FTL jumps? Do ships need to refuel before another jump, or are multiple jumps possible before refueling, just requiring time to calculate the new jump? Is the fuel for such a jump 'easily' acquired from asteroids, gas giants, or stellar surfaces; or does it require complex infrastructure to mine or produce? $\endgroup$
    – Michael Richardson
    Jun 29, 2022 at 15:50
  • $\begingroup$ @MichaelRichardson The range of the FTL jump is essentially any given nearby star, there isn't a set limit but the rule of thumb is the shorter the jump the better, due to limitations related to stability and energy requirements. In short the longer the drive is on the higher the risk of catastrophy. As for the energy and matter needed, I figured that everything needed could be obtained from the stars themselves, through the use of rudimentary dyson swarms. $\endgroup$
    – JuimyTheHyena
    Jun 29, 2022 at 17:44
  • $\begingroup$ @JuimyTheHyena Define "nearby". As in, give us a maximum tolerable distance for regular space travel. Right now, for all we know it could be 5 light-years or 5000. Or, better yet, you can tell us the average distance after which a catastrophe occurs (or time if you define a typical cruising speed). This would let us approximate the chance of catastrophe y from any distance traveled x as p = e^(-x/µ), where µ is the average travel distance before a crash occurs. Then, we can infer how much risk people would be willing to take in different scenarios (e.g. moving goods vs waging war) $\endgroup$
    – Ethan Maness
    Jun 29, 2022 at 19:49
  • $\begingroup$ @EthanManess hmmmm, I have to admit...I am not sure about the maximum tolerable distance, since I figured that it could increase given innovation...I think that pheraps 5000 light years would be a fair enough maximum tolerance. $\endgroup$
    – JuimyTheHyena
    Jun 30, 2022 at 8:48

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That's a good start for space hazards.

Even though humanity has only dipped our toes into space, we are still very concerned about radiation. Not only is there a cancer risk, but there as also a risk to electronics. Things like single event effects can eventually render electronics useless.

In addition to radiation, nebulae are also to be avoided. These ionized gases may react with the spaceship but also increase the temperature to an unacceptable level.

More things can be concerning: stellar activity (as you have identified), gravity wells for large stars you cannot get out of, potential effects of things like stellar wind, and not to mention simply monitoring for new objects coming into view as you speed by. Yes, space is big, but you will feel like a soon-to-be-dead fool if you miss an encounter with a planet that knocks you off course or you manage to hit something.

Edit: We should also acknowledge that we just have not gone very far into space, and there may be more things to worry about that we simply don't know or cannot totally answer here. Maybe cosmic rays outside the heliopause become a nuisance. Maybe wandering, primordial black holes are super common. We just don't know!

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  • $\begingroup$ One thing to note: When you're going FTL, planetary gravity (or even stellar gravity) is really not much of a problem—Earth only bends passing photons by about 0.0000001 degrees. $\endgroup$
    – Ethan Maness
    Jun 29, 2022 at 20:28
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Flipping Black-holes.

They normally have predictable rotation, an accretion disk that behaves in a nice orderly fashion and an ejection of x-rays and very fast ions in regular and expected directions at the poles. You'd think that staying away from the cones of space that line-up with the axis of rotation would protect you from all that high energy nastiness ejected, but....

Sometimes they flip magnetic fields N-S to S-N, sounds trivial right? Not so. The energy output vastly increases and the direction it's directed in - well, space in any direction can suddenly become very hot and uncomfortable for any ship or planet or star-system caught up in it.

These sudden fits of super-brightness in the X-Ray, UV and relativistic ion energy-output in all directions are quite unpredictable and without any apparent obvious warning - if you're within a few tens/hundreds of light-years and one of these things happens - then all bets are off for survival.

Primordial black-holes.

These create a special hazard as they may not have any accretion-disk and would thus be invisible - depending on the amount of Hawking radiation they emit - inversely proportional to their size.

The Little ones can look like harmless wandering stars that suddenly grow in the magnitude of the radiation they release then essentially explode in a vast cataclysm of energy. The big ones, can be more-or-less invisible until they perturb your solar-system's planets orbits enough to ruin all your plans to visit. Don't smack-into one.

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  • $\begingroup$ As I understand it this is only dangerous if the black hole has an accretion disk? $\endgroup$
    – TheDyingOfLight
    Jun 18, 2022 at 17:14
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    $\begingroup$ Most do, unless you want to count as another hazard the encountering of a primordial one which didn't form by the usual stellar-collapse. They might just be tricky to see and predict too. @TheDyingOfLight $\endgroup$
    – Escaped dental patient.
    Jun 18, 2022 at 17:26
  • $\begingroup$ The rate of Hawking decay is far, far, too slow for black hole explosions to be of any concern. We have literally never observed one. Not to mention the explosions themselves are pretty small by cosmic standards—less than 0.3% as bright as the Sun (which is notably non-lethal even from a distance of 8.3 light-minutes). By comparison, supernovas are far more common and 1 billion trillion times more powerful, and even then you would pretty much never have to worry about running into one. $\endgroup$
    – Ethan Maness
    Jun 29, 2022 at 20:15
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Gravity and radiation might make them difficult to contend with, but who cares. Because if you're only moving to close stars you won't be getting anywhere near them.

So they shouldn't be problems.

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  • $\begingroup$ I honestly figured that you’d need to reach into each start system to refuel/restock on minerals and other things needed for the trips. Besides that I think that the ships would need to move through the gravity wells in any case to get clear of them before jumping again. $\endgroup$
    – JuimyTheHyena
    Jun 18, 2022 at 17:34
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Just yawning stretches of emptiness. Perhaps civilisations like ours in the spiral arms can only really hop along the arms. Travelling large void areas would just take too long. Perhaps all the interesting stuff is just too far away.

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STL travel is limited to shielding concerns. Do the figures about how much heat you have to get rid of per square meter, punching through vacuum at 10% of c, with a typical gas density of 1 atom of H per cubic centimeter.

FTL happens in some form of hyperspace. Hyperspace is connected differently. Hyperspace is generally more compact, but is folded weirdly so that points that are close together in hyper map to large disances in normal space. But the folds have culdesacs. The folds have large areas where the normal space mapping is in intergalactic space.

In Pournell's universe, transitions between stars happens via Alderson drive. The departure point and the target point have to match both solar gravitational potential energy and solar radiation intensity. This means that not all stars have a point of connection between them.

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