OTU Only: Mapping the Local Arm

[robject]

The "Local Arm" is the galactic arm, in the middle of which Charted Space sits.

I've traced sectors along the Great Rift rimward to the "Great Abyss" region (or whatever you want to call it) halfway to the edge of the arm, but haven't gone further.

Today, though, I started thinking about the rimward border of the local arm. What does it look like? A flat demarcation between "regular density" and "extra rift density"? Or a gradual but regular decrease in density, over the space of a few sectors, until we're in the rift?

I think I like to keep my options open: it can be like it is in the Great Rift with sudden "dropoffs", but could also be gradual, depending on what you want.

I also think that that edge is not a straight line running through the sectors. I tend to prefer that it is rather irregular, with sector-sized dips and promontories, making for varied and interesting "terrain".

Thoughts?

 

[Hemdian]

Have you looked at the Zhodani Core Route? (Although Chris Lineham's site is gone the data is included on Travellermap.com.) That cuts across multiple arms and the spaces in between ... albeit without much width.

My gut feeling (based on no evidence at all) is that across a wide boundary, some areas will have sudden drop offs whereas others will have a more gradual petering out. And some areas where there is a sudden drop off may have higher than normal density right up to the 'cliff'.

 

[whulorigan]

The "Local Arm" is the galactic arm, in the middle of which Charted Space sits.

I've traced sectors along the Great Rift rimward to the "Great Abyss" region (or whatever you want to call it) halfway to the edge of the arm, but haven't gone further.

Today, though, I started thinking about the rimward border of the local arm. What does it look like? A flat demarcation between "regular density" and "extra rift density"? Or a gradual but regular decrease in density, over the space of a few sectors, until we're in the rift?

I think I like to keep my options open: it can be like it is in the Great Rift with sudden "dropoffs", but could also be gradual, depending on what you want.

I also think that that edge is not a straight line running through the sectors. I tend to prefer that it is rather irregular, with sector-sized dips and promontories, making for varied and interesting "terrain".

Thoughts?

Keep in mind that while the space between the galactic arms is of lower stellar density than within the arms proper, the "arms" are more an "observational" phenomenon than a purely structural one. The spiral structure is believed to be the result of a "density wave" within the galactic disc. Since the areas of higher gas-density are also naturally regions of higher star-formation rates, they appear "brighter" and "bluer" than the rest of the disk, where the remaining (older) stars tend to be dimmer and redder.

So between the spiral arms, while the region does have a lower stellar density than the arms proper, the stars have a much higher degree of probability of being dim red stars (and presumably white dwarfs), whereas within the higher-density arms where star formation is being driven by gas-compression, there are many more younger, brighter and "bluer" stars (which is why the regions stand out as visible "arms").

Theory:
"http://en.wikipedia.org/wiki/Density_wave_theory "
"http://en.wikipedia.org/wiki/Spiral_galaxy#Origin_of_the_spiral_structure "

Nice animation:
https://www.youtube.com/watch?v=c5Us-jonCLA

 

[robject]

@Peter: yes, Cliff's data is instructive. He uses a fast drop-off from standard density to sparse.

And @Whorl's note is an interesting and tidy explanation of what arms *are* and why the spaces between look dimmer.

It's almost more intense having a sea of sparse, dead or uninhabitable systems, than to have a lack of stars altogether.

 

[whulorigan]

It's almost more intense having a sea of sparse, dead or uninhabitable systems, than to have a lack of stars altogether.

As an aside, another interesting thought (particularly for a campaign involving one or more "ancients" connections (either capital A- or lowercase a-)) that often get overlooked are the island-like Globular Clusters in the Galactic Halo (above/below the galactic plane). You certainly cannot get to them using standard Jump Drive (but perhaps using a Skip- or Leap-Drive you could), but one wonders what might be (or might have been long, long ago) lurking there in those clusters, staring down from above the galactic plane from a high vantage point, observing, planning, . . .


Globular Clusters
http://en.wikipedia.org/wiki/Globular_cluster

 

[robject]

And for my purposes, just identifying the sector of space I've worked is an interesting problem. How do I define its position? As an offset from Core Sector?

I think travellermap.com has an Imperiocentric coordinate system, doesn't it?

 

[whulorigan]

And for my purposes, just identifying the sector of space I've worked is an interesting problem. How do I define its position? As an offset from Core Sector?

I think travellermap.com has an Imperiocentric coordinate system, doesn't it?

Yes. The coordinate system is based upon the planet Reference/Core0140 as the Origin. Core Sector is Sector [0,0], Fornast is [0,1], Dagudashaag is [-1,0], Massilia is [0,-1], Lishun is [0,1], Vland is [-1,1], etc.

Simply decide the number of sectors "x" Spinward/Trailing of Core, and the number of sectors "y" Coreward/Rimward of Core, and call it Sector [x,y].


Note that Sol is about 190 Sectors from the Galactic Core. The Perseus Arm is about 50 Sectors Rimward from the Orion Spur (where Charted Space lies).

 

[Lycanorukke]

staring down from above the galactic plane from a high vantage point, observing, planning, . . .

....regarded this earth known space with envious eyes; and slowly, and surely, they drew their plans against us.
WoTW - Eve of the War

 

[JimMarn]

As an aside, another interesting thought (particularly for a campaign involving one or more "ancients" connections (either capital A- or lowercase a-)) that often get overlooked are the island-like Globular Clusters in the Galactic Halo (above/below the galactic plane). You certainly cannot get to them using standard Jump Drive (but perhaps using a Skip- or Leap-Drive you could), but one wonders what might be (or might have been long, long ago) lurking there in those clusters, staring down from above the galactic plane from a high vantage point, observing, planning, . . .


Globular Clusters
http://en.wikipedia.org/wiki/Globular_cluster

It is possible, Jump 1 or Jump 2 had been invented there long before it was invented in the galaxy... then they realized the galaxy was too far away for Jump drive to get them there. What affect that would have on their society could make for some interesting adventure hooks.

 

[Ulsyus]

So between the spiral arms, while the region does have a lower stellar density than the arms proper, the stars have a much higher degree of probability of being dim red stars (and presumably white dwarfs), whereas within the higher-density arms where star formation is being driven by gas-compression, there are many more younger, brighter and "bluer" stars (which is why the regions stand out as visible "arms").

Would the likelihood of the formation of gas giants in these be similar to in the denser arms? If so, then in the "dead" space between the arms it may be possible for "deep space" vessels to refuel on their way between the arms...

 

[whulorigan]

Would the likelihood of the formation of gas giants in these be similar to in the denser arms? If so, then in the "dead" space between the arms it may be possible for "deep space" vessels to refuel on their way between the arms...

Possibly. Gas Giants are actually theorized to form by a different process than stars, despite the fact that they both have atmospheres comprised primarily of hydrogen. Stars form primarily by gas accretion and gravitational-compression of a gravitationally collapsing gas cloud. Gas Giants tend to form (as far as we know) around a dense, rocky, and sufficiently large proto-planetary core at a sufficient distance from the central star so that hydrogen and "ices" do not get boiled away from the atmosphere, and continue to accrete and compact thru gravitation. Such Jovian or Neptunian worlds may form within a system and be gravitationally "ejected" from that system at an early stage of the system's development thru a close encounter with another body. Or it may be possible that a Gas Giant could form independently under certain conditions.

Since planetary sized bodies are almost impossible to detect with today's equipment (except when in orbit around a star creating some type of "wobble"), I would say there is little evidence one way or the other as to the number of "Rogue-Jovians" or "Rogue-Neptunians" floating in the interstellar medium. Some theories even suggest that they may be as common as stars. Another thing to remember is that former (now dead) stars (i.e. white dwarfs) most likely populate the region between the arms as well (they are very difficult to detect), and such stars may have cold Jovians and Neptunians in their outer orbits.

Another possibility is that there may be Brown Dwarfs in abundance, some of which will be older Y-Type Brown Dwarfs. Y-type dwarfs can have atmospheric temperatures corresponding to "room-temperature", and might be able to be skimmed.


(Actually, the current exo-planets that are being discovered are turning a lot of planet-formation theories on their heads, so I would say you have precedent to do what you want in this regard )

 

[Ulsyus]

That's really good stuff to know in terms of building a moderately-hard-science game. So pulling it all together, and extrapolating a little, and using some poetic licence, we could describe the space between the arms as having a lower density of stars, but those that are there have a relatively lower luminosity than the arms due to density and type differences. The stars that are there are likely to have sufficient gas giants present to allow for refueling when traveling inter-arm, and there would even be some systems with habitable planets, or at least planets that by the time of 3I are inhabited.

I might have to dig out 2300 and do some work on what a few colonies, set up between Terran discovery of the jump drive and the establishment of the Rule of Man, would look like later on...

Not quite the Clements Sector, but if enough time passes then it may pass for something interesting...