Need an Astronomer

(Disclaimer: I used to know a lot about astronomy, but I can't seem to answer my own dilemma. Brain fart.)

My sci-fi epic is set in/around the Earth years 2700-3100 (need to double-check). Humans have just then been able to start exploring the Milky Way, when they stumble upon a cluster (right word?) of systems sporting numerous intelligent civilizations who have just finished a war among themselves. Naturally, they're like "HA, aren't you guys late to the party?" and the "story" itself is records of the conflict given to human historians.

I know that it's very unlikely (Drake equation, Fermi paradox and all that) to have a bunch of intergalactic civs spring up right next to each other, but this is a story, and putting that aside, I wanted it to have some elements of realism. I'd like to know what stars, if any, are near enough for future humans to feasibly reach, and, perhaps, discover life at all. If I have to make up my miracle cluster, that's fine too, I'd just like to know about how far away it should be for travel purposes. (Maybe average distance between star systems would be useful (for the cluster), if that's calculable?)
(Of special note, if it matters, the human's technology is far below that of the aliens. As I said, the humans just figured out how to do this, while these aliens have had it for at least a few hundred years, and are fighting wars with each other.)

 

Cluster is not the correct word because it implies a globular cluster, which is a specific astronomical object. There are about 150 of them in the galaxy, but all are very far away (the closest being about 7500 light years.) There are many smaller groups of nearby stars though (The Pleiades are only about 500 light years away, but too young to host life.) That may be beneficial because you don't want to get so close that humans will be able to map the worlds any time soon. We know of several planets within 100 light years that are in the right distance from their stars and we'll start to analyze their atmosphere in 2018 when the James Webb Telescope goes up.

Tightly packed groups of stars are a prime target for SETI because of the proximity of the stars. Close neighbors mean shorter initial trips. They also tend to mix gas and dust with each other, which can easily cross-contaminate planets. There are two leading theories of how life originated on Earth: Abiogenesis and Panspermia, the latter having been a fringe theory but now becoming way more likely. It's the idea that life may have originated elsewhere and come here.

Red dwarfs are always interesting from a biological point of view. In the early part of their lives, they throw really wild temper tantrums. This is because they're undergoing the same fusion process as the sun, but has far far less gravity to hold all of that energy in, which makes it more volatile. But, once they've cooled down a little, they burn very consistently for trillions of years. They're also hard to see, they glow mostly in infrared, which the galaxy's just can obscure.

Binary stars would only be a problem if they were about the same size or very close together. For example, Proximar Centauri would have almost no gravitational impact on anything in orbit around AB Centauri both because of how small it is and how far away it is from the others.

The distance I'd guess that you'd have to go out to discover a cluster of low mass stars that we currently either don't know about or don't really think twice about is maybe 300 light years. Our star is pretty average in terms of nearest neighbors, stars are usually more than a few light years apart, but closer than ten.

 

The Kepler web site is going to give you a nice list of planets and solar systems to choose from if you want reality.

You may want to look at them but develop your own fictional part of the galaxy.

As far as travel, pick a speed to fit your story then adapt the travel to it.

For example, I chose 10% of light speed. That means it takes 40 years to get to the nearest star, Proxima Centauri. It's more realistic that in the not too distant future there will be technology to travel that fast and it avoids most of the issues of time one gets if one travels closer to light speed.

But it doesn't sound like that will do for your story so you'll need to go with purely fictional travel: worm holes or space warps are common ways around interstellar travel distances.

 

Yeah, I had figured if the aliens had to give a brief explanation as to their warp/hyperspace technology, it would be "a thing in/on the ship punches a wormhole in space time, which sucks the ship in and spits it out at these carefully registered coordinates". Depending on the type of ship and quality of its tech, this process could range from harmless to haphazard to having serious repercussions on the crew... and the ship. I have no clue how one even could generate a wormhole or even if it would be possible, so I think that's as deep an explanation as warp travel needs.

This is actually quite helpful, it certainly put a lot in scope for me. I kind of figured it would be in the range of hundreds of light years. Thank you.

I'll be sure to update from time to time, as I'll probably have more questions as I go.

 

Interesting, I use a form of subspace travel (lots of theoretical quantum physics
that I don't fully understand for my alien species, but it has its limitations
taking hours, days, months, etc. the further you want to travel. But short jumps
appear to happen instantly. Just a fancy FTL travel with a bit of scientific theory,)
Suppose using a different dimension beneath space has limits too. But would not
destroy a planet if you happen to be close, with a nasty gravity well.
(Star Treks Warp travel would literally crush planets, if it were used in a real
application.)

As for where to find planets, well the simplest way is to see something blocks the light
emitted from a given star you are looking at (that is how we do that now). The Milky way
is 100,000 light years across, which is pretty damned big in terms of size with plenty of
stars to simply throw a dart and probably hit a distant solar system that is unknown
to us as of yet. So you have a whole galaxy that is unknown to pick from, and create
your Alien Species from.
Hows your chemistry for creating plausible aliens? Mine is pretty narrow, carbon and
silicon are the only elements I can think of that are stable enough to support DNA
structure (but I bet there are a whole slew of others that could offer more complex
and interesting properties to the equation). Then again you could have a whole race
based from Uranium for all I know (Tell your human travelers to pack their lead
lined panties.) Though just because they share a common building block does not
mean they cannot appear to be some strange things we only imagine.

Hydrogen, Helium, and Oxygen are oddly abundant in the galaxy. So some form
of fusion should be on the table for your humans for travel/power. You can use
light as a form of propulsion, but it would take far too long to get up to any kind of
speed.

Plenty of resources out there to help you out with what you need.
Good luck, and have fun.

 

In my little star group, I began to wonder how their ships would actually be powered. Solar is practical for little ships, but for bigger ones I went with the classically sci-fi answer of "some kind of synthetic energy crystal". Although, I wanted to give this place a sense of history... I thought of our own Industrial Revolution and what things were like before we started coming up with modern, more efficient sources of energy (which, sadly, we don't use enough).
I thought, "What was this sector's equivalent of a coal boom?"
I had the idea of deploying "collector ships" and squads of fighters equipped to collect the gas/dust in nebulae, you know the {even crazier space dust} that makes stars and stuff, which through their fancy space tech could be converted into fuel for ships. I thought of different companies having fierce rivalries, to the point where the collection fighters would actually re-equip their weapons and skirmish amongst the clouds and nebula storms. These "storm-riders" were seen as braver than brave, and inspired a whole generation of spacers, before synthetic energy was developed and put them out of business.
While I love it, however accurate, and am definitely keeping it, I'm kind of curious as to how accurate it is. I'd imagine nebula is mostly hydrogen, which could definitely be a fuel source in some way.

 

Depends on the type of nebula. A lot of them are mostly hydrogen, but they're so big that you could postulate finding anything you want. If you do go with hydrogen, for the amount of energy you're looking for you'd probably need to figure out proton-proton fusion.

My big question would be--going all the way out to a nebula, scooping up a bunch of stuff, and trucking it all back to your homeworld seems like an awful lot of work. To continue with hydrogen--why not just get it from all the water ice floating around your home system in comets? That seems much, much, much easier. In general I'm not sure what you would find in a nebula that wouldn't be a lot easier to get from somewhere close to home. Unless you need ungodly amounts of the stuff, like more than several Earth masses worth.

Overall I like your premise and none of it's really a dealbreaker for me (full disclosure, I'm not a hard sci-fi purist). Just some things to think about...

 

The densest nebulae have approximately

• 1 million particles per cubic centimeter
• 1 million million particles per cubic meter
• 2500 million million particles per Olympic Swimming Pool (2500 cubic meters)

2 grams of molecular hydrogen would require 60 thousand million million million particles (24 million Olympic swimming pools worth of space)

If you're certain that you want to use planetary nebulae, then you're going to want to come up with some sort of Phlebotinum/Unobtanium that you can't easily get anywhere else, because if all you want is hydrogen, then you can make more than that just by putting taping a wire to a battery and dropping it in a glass of water (don't try this at home).

The spaceship in my SF work uses black holes

Black holes give off energy in the form of Hawking Radiation, and smaller black holes give off more power (energy per unit of time) than larger black holes (which burns off the black hole's mass, making it hotter, making it lose even more mass and burn even hotter... until you end up with a runaway explosion).

A black hole that starts out with the mass of the Empire State building (331,000 tonnes) would have a lifetime of 96.6 years and would start out with a power of 777 kilotons (≈40 Hiroshima bombs) per second.

A black hole with 50 years left would have a mass of 265,750 tonnes and would burn at 1.2 megatons (≈65 Hiroshima bombs) per second.

A black hole that puts out 56 megatons (≈ the Tsar Bomba) per second would have a mass of just under 40,000 tonnes and a lifetime of just under 2 months.

 

Nice sci fi material @Cave Troll.

 

Nebulas are so not dense that if you were right in the middle of one, you probably wouldn't even know it. They are bright and fuzzy because of what's in them and how monsterous they are. The horsehead nebula for example is about 5 light years across. Most of nebulas are hydrogen, but their colors come from their metalicity. All of these chemicals are known to science though, heavy atoms are created by supernova and neutron star collisions, neither are powerful enough to form exotic matter. We can also see what they are made of across the universe (through spectroscopy,) so there is no need to go out and search.

There are way easier ways to get huge amounts of hydrogen. Most stars have huge swarms of comets swarming around them. Unlocking hydrogen from ice is far easier than creating some EM maw to suck in atomic hydrogen. Hydrogen (and even heavy elements) probably wouldn't be very useful. Nuclear energy just isn't very powerful. Nuclear fusion converts less than 1% of the mass into energy. A quantum annihilation converts all mass into energy, which is why black holes and antimatter are nice for scifi. There is also unfathomable amounts of energy stuck in the fabric of spacetime itself, if you could tap into that, it could take you anywhere you want to go. So maybe your "industrial revolution" would be either figuring out how to easily make antimatter for annihilation, or tapping into the quantum foam. Both are far beyond our current capability, but not impossible.

 

Thanks.

I try to find somethings that can be kept somewhat in the realm
of plausibility.

 

I love this discussion already.
That being said, the thing with the nebulae is pretty fascinating. There was much I did not know.
(If anyone wishes to see a WIP map of my star group, just PM me.)

 

(Just wanted to make a quick comment, not a nitpick, just a response: there was one star system* that really monopolized the industry because it was situated around a pretty massive nebula; they didn't have exclusive rights, however, and the competing companies actually collected enough to split it into two smaller nebulae. Very science-fantasy, but I like it, and I'm glad you do.)
(*Star systems, in my work, seem to average 4-9 planets, only one bearing intelligent life. Seemed like good odds. In-universe, people typically just refer to that planet, rather than the system itself. Like, if you were visiting Earth, for example, you'd just say "I'm going to Earth" not "the Terran System" because it's obvious which planet you're likely visiting.)

 

Using this map (great map by the way) Tau Ceti is your best bet, circa ten light years away. It is a yellow star dimmer than our sun.

Red dwarfs have the issue of tidal locking, and anything larger than our sun have the issue of solar winds that strip away the magnetic field and atmosphere (and a short lifespan).

 

Twelve light years but who's counting.

I'm 3/4 through Aurora by Kim Stanley Robinson.

 

You don't need expert assistance here; you can see for yourself.

 

I bow to your greater knowledge