100D Limit and Mass of Object

[Terry Mixon]

A fair bit of discussion has happened about the 100D limit and whether or not the mass of the object has any bearing on that. The Core Expeditions has a little blurb about a very dense star, that actually finally clarifies that mass does have a bearing on the jump limit.

While I’m uncertain that this actually has any bearing on whether or not the galactic core/bulge could have its own influence on jump mechanics, it does in fact, give credence to the thought that mass has to play a role whereas before that really wasn’t clear so far as the rules were concerned.

Thoughts?

 

[Vormaerin]

The 100D limit has always been a gameplay fudge in place of having to calculate the mass of a star or planet and then determine its gravitic field. The fictional science underlying it was always the gravity well, but 100D was "close enough for government work" as they say. Same reason the game uses volume instead of mass for how big ships are. Just easier to calculate.

 

[GabrielGABFonseca]

A fair bit of discussion has happened about the 100D limit and whether or not the mass of the object has any bearing on that. The Core Expeditions has a little blurb about a very dense star, that actually finally clarifies that mass does have a bearing on the jump limit.

While I’m uncertain that this actually has any bearing on whether or not the galactic core/bulge could have its own influence on jump mechanics, it does in fact, give credence to the thought that mass has to play a role whereas before that really wasn’t clear so far as the rules were concerned.

Thoughts?

For what it is worth, the WBH also states mass influences it. The article on Jump Drives MWM wrote for the original JTAS also mentions that. They all point out that the 100D limit is a "rule of thumb" to ensure safe jumping, as a Watsonian (in-universe) explanation.

The Doylist explanation, as Vormaerin said, is just that going with 100 Diameters is simpler than having to calculate the gravitational gradient of every body your players wish to jump to.
(The math is actually not that hard, but done for every jump it accumulates into annoying faff).

 

[Terry Mixon]

So, if mass is at the bottom of it, wouldn’t that mass of the galactic core/bulge be problematic for jump travel to the core? It could even cover a large area out from the core. I’m not strong enough in math, but a significant portion of the mass in the galaxy is in the core.

 

[Limpin Legin]

I don't know if anyone knows what is at core. It could just be that there is less empty parsecs per subsector. Dosen't necessarily imply that there are more stars within a 100D - 300D volume. If there are, then that would logically form no-go zones for x-boats, etc. But the whole reason for inventing Jump-drives is that everything is so spread out - if everything was closer together coreward, then interstellar travel could more likely be accomplished without Jump-drive?

 

[rinku]

As far as the core goes, at any one point you're still only likely to be within 100D of a few massive objects. There may be thousands of stars within a light year, but a light year is a long distance.

However, lining up any long jumps becomes problematic.

Edit: Okay, I looked it up, and at the galactic core you're looking at average separations of about 1000AU - call it a light week. That compares to average separations of around 5 light years out where we are. As Limpin Legin suggested, practical sublight travel could exist.

But what you WILL have are a lot more multiples, a lot more star creation and death (bigger stars will be more common, and those live fast and die young) and a whole lot more radiation.

As far as subsector maps go... forget empty hexes. There are none. What you're looking at are how many millions of stars there are in a hex.

 

[hopsnbaer]

There is likely a super massive black hole at the center of the galaxy.

Sagittarius A* - Wikipedia

en.wikipedia.org

Could be an issue.

 

[CordwainerFish]

I just can't see anything but mass being relevant, via the same gedankenexperiment by which Galileo concluded that heavy objects fall at the same speed as light ones. And Traveller is at the end of the pool that's supposed to be occupied by people who like physics and math...

 

[hopsnbaer]

I think it would be 30 or 40 parsecs so not a huge issue. I expect there will be systems that can't be reached by J-Drive.

 

[rinku]

I think it would be 30 or 40 parsecs so not a huge issue. I expect there will be systems that can't be reached by J-Drive.

Not sure what you mean by "30 or 40 parsecs" here. The jump shadow?

Sagittarius A* seems to have an angular diameter or around 50 million km. So the normal jump shadow would be about 5 billion km, which is only 0.000162 parsec. Even if you applied a "high density modifier" for a black hole of (as an example) x1000 (to make it 0.162 parsec), the jump shadow would still be contained well within one hex.

 

[hopsnbaer]

Not sure what you mean by "30 or 40 parsecs" here. The jump shadow?

Sagittarius A* seems to have an angular diameter or around 50 million km. So the normal jump shadow would be about 5 billion km, which is only 0.000162 parsec. Even if you applied a "high density modifier" for a black hole of (as an example) x1000 (to make it 0.162 parsec), the jump shadow would still be contained well within one hex.

I took 100 Diameters from the sun which is about 1 AU. Sagitarius A is estimated to have the mass of 4.3 million of our suns, so 4.3 million AU and rounded significantly up. So maybe 20 to 30 Parsecs. The point is there are probably a number of systems that cannot be reached by jump even if it is only 20 parsecs.

As far as the game is concerned you are probably closer to RAW.

Mine was only a very rough estimate, and while I am not an Astrophysicist, I did stay at a Holiday Inn Express last night.

 

[Terry Mixon]

I took 100 Diameters from the sun which is about 1 AU. Sagitarius A is estimated to have the mass of 4.3 million of our suns, so 4.3 million AU and rounded significantly up. So maybe 20 to 30 Parsecs. The point is there are probably a number of systems that cannot be reached by jump even if it is only 20 parsecs.

As far as the game is concerned you are probably closer to RAW.

Mine was only a very rough estimate, and while I am not an Astrophysicist, I did stay at a Holiday Inn Express last night.

Wikipedia says, “Stellar density at the galactic core is extremely high, with estimates of roughly 105 to 107 stars per cubic parsec within the central parsec, compared to only 0.14 stars per cubic parsec in our solar neighborhood. At this density, stars are separated by light-weeks rather than light-years, resulting in a night sky with 200 times more light than a full moon.”

Makes me wonder if that much mass in close proximity would count as a single source if big enough or closely spaced.

 

[hopsnbaer]

Wikipedia says, “Stellar density at the galactic core is extremely high, with estimates of roughly 105 to 107 stars per cubic parsec within the central parsec, compared to only 0.14 stars per cubic parsec in our solar neighborhood. At this density, stars are separated by light-weeks rather than light-years, resulting in a night sky with 200 times more light than a full moon.”

I figure It could be rough finding a straight path through without getting pulled out of jump.

 

[Terry Mixon]

I also found:

“There are around 10 million stars within one parsec of the Galactic Center, dominated by red giants, with a significant population of massive supergiantsand Wolf–Rayet stars from star formation in the region around 1 million years ago. The core stars are a small part within the much wider central region, called the galactic bulge.”

And “The Milky Way's galactic bulge has an estimated stellar mass of approximately 1.5×1010 to
2.0×1010 solar masses. It represents about one-quarter of the Milky Way's total stellar mass. This central component is mostly a bar-shaped structure, with <10% of its mass in a "classical" bulge.”

All that mass in close proximity seems like it would make for a combined jump limit of some sort.

 

[hopsnbaer]

I also found:

“There are around 10 million stars within one parsec of the Galactic Center, dominated by red giants, with a significant population of massive supergiantsand Wolf–Rayet stars from star formation in the region around 1 million years ago. The core stars are a small part within the much wider central region, called the galactic bulge.”

Did you also stay at a Holiday Inn Express?

 

[Terry Mixon]

Did you also stay at a Holiday Inn Express?

Yes. Yes, I did.

I also added more information to both those posts, so humor me and check them out.

 

[rinku]

It's all quite academic, but I think it is safe to say that JUST having all those red giants (with their MASSIVE jump shadows under standard rules) in close proximity is likely to prevent long distance jumps and fast travel. You'd be having to make a lot of zig zag sub J-1 hops, and taking weeks in real space to get from 100D to a fuel source (assuming there are any. Gas giants in stable orbits might be hard to come by).

You really would not need to add any extra rules to make it harder, and if you did it would basically mean interstellar travel was limited to sublight anyway. On the other hand, you might be able to get from system to system in a matter of months using M-Drive, and all that gravity would mean you're probably never going to hit the dropoff.

 

[Condottiere]

Space Sargasso Sea.

Only way to traverse it, is slower than light speed propulsion.