Scrunched Known Space

[Kakistocrat]

The overall completeness of the GCNS to M8 at 100 pc is probably better than 95%.​

I’d misinterpreted “M8” in the previous post. It doesn’t refer to measured parallaxes, but rather to stellar classifications — the “overall completeness of the GCNS to M8 at 100 pc” refers to stellar objects down to the M8 type, so the probable 95+% completeness within 100 pc doesn’t apply to the M9 spectral class and the L, T, and Y spectral classes.

 

[Straybow]

Gaia's 331,312 objects within 100 pc = 331,312 / 3,141,593 pc³ = 0.105 stars / pc³
Not that far off from my assumption based on local density of 0.120 stars / pc³
Way lower than aramis' 1/2.507 = 0.399 stars / pc³

 

[Spinward Flow]

Gaia's 331,312 objects within 100 pc = 331,312 / 3,141,593 pc³ = 0.105 stars / pc³

Volume of a sphere = 4/3*pi*r³
4/3 * 3.14159265 * 100*100*100 = 4,188,790.2 (check my math)
331,312 / 4,188,790.2 = 0.079094913848872 stars per parsec³

Now, granted, that's using a spherical shape with a spiral disc galaxy (slightly warped) running through it, so there's going to be a lot of "empty space" above and below the main disc of the galaxy where most of the stars are to be found.



If we (vastly over)simplify things down into a 2D circle (which you can then hex map on paper), we get the following (somewhat obviously ridiculous answer):

Area of a circle = pi*r²
3.14159265 * 100*100 = 31,415.9265 (check my math)
331,312 / 31,415.9265 = 10.54598851318296 stars per parsec²

So simply "flattening the volume" of space is DEFINITELY not the answer!
Going from an average of ~10.55 stars per parsec² in 2D down to an average of ~0.08 stars per parsec³ makes for quite a large swing in average density (a difference of over x1000!) when looking at a 100 parsec radius around Terra in the Sol system.



This has been yet another example of how manipulating questions to generate averages can quickly lead to "Lies, Damned Lies and Statistics" when asking questions that are not exactly "helpful" in getting at the answers you might be looking for, since the shape of distribution for the stars within a 100 parsec radius is not "average in every direction" in an equal fashion.

Even if you assume that there is "1 star system per 12.5 parsecs³" (which sounds like a lot) ... as soon as you do the volume math for spheres, you start winding up with evenly distributed "marbles to stack in all directions" that are only ~1.45 parsecs in radius each ... meaning that individual star systems would be ON. AVERAGE only ~3 parsecs/~10 light years apart (because, 2 radii) from each other in all directions (on average), which for us Travellers would mean that J3 would become the "go to" drive system to reach the majority of destinations.

 

[Straybow]

Yeah, forgot 4/3...

But 331,312 objects includes exoplanets, white and brown dwarfs, and "objects without a spectral type" (which is a very puzzling description). The 10 pc sample has this distribution:

246 Singles
69 Binaries = 138
19 Triples = 57
3 Quads = 12
2 Quints = 10
________________
339 Systems with 463 stars* (includes everything except exoplanets)

Average is 1.37 stars* per system. In addition, the sample includes 77/540 exoplanets = 14%. Gaia has returned a total of 297 exoplanets as of 2022, but I'm not going to parse that data to figure out how many are within 100 pc. Let's assume all of them, since exoplanets can be tough to spot.

331,312-297 non-exoplanet objects /1.37 per system = 242,363 stellar systems
242,363/(4π/3*100³) = 242,363/4,188,790 = 0.058 systems per pc³
Or flip it over and get 17.28 pc³ per system.
This is far more sparse than our local 5 or 10 pc radius neighborhood, by a factor of 2.

Anyway, 11k systems would then fit into ³√(¾·11k·17.28/π) = 35.7 pc radius

 

[Spinward Flow]

Anyway, 11k systems would then fit into ³√(¾·11k·17.28/π) = 35.7 pc radius

 

[Dragoner]

Yeah, forgot 4/3...

But 331,312 objects includes exoplanets, white and brown dwarfs, and "objects without a spectral type" (which is a very puzzling description). The 10 pc sample has this distribution:

246 Singles
69 Binaries = 138
19 Triples = 57
3 Quads = 12
2 Quints = 10
________________
339 Systems with 463 stars* (includes everything except exoplanets)

Average is 1.37 stars* per system. In addition, the sample includes 77/540 exoplanets = 14%. Gaia has returned a total of 297 exoplanets as of 2022, but I'm not going to parse that data to figure out how many are within 100 pc. Let's assume all of them, since exoplanets can be tough to spot.

331,312-297 non-exoplanet objects /1.37 per system = 242,363 stellar systems
242,363/(4π/3*100³) = 242,363/4,188,790 = 0.058 systems per pc³
Or flip it over and get 17.28 pc³ per system.
This is far more sparse than our local 5 or 10 pc radius neighborhood, by a factor of 2.

Anyway, 11k systems would then fit into ³√(¾·11k·17.28/π) = 35.7 pc radius

The only thing I would add to this is that there are clusters, the distribution is not even. Something to think about.

 

[aramis]

But 331,312 objects includes exoplanets, white and brown dwarfs, and "objects without a spectral type" (which is a very puzzling description).

It shouldn't be... The expanded Morgan-Keenan system is currently OBAFGKMLTY - including brown dwarves. Only M runs past 9; M runs to 19, but L overlaps M somewhat. Most also list the Yerkes size. (the roman numbers


OBAFGKMLTY are normal metallicity,

Class	Temp (K)	Notable diagnostics
O	28k⋯50k
B	10k ⋯ 30k
A	7500 ⋯ 10k
F	6000 ⋯ 7500
G	4900 ⋯ 6000
K	3700 ⋯ 5200
M0M9	2400 ⋯ 3700
L	1400 ⋯ 2600
T	450 ⋯ 1400	Methane dominant
Y	200 ⋯ 700
—	—	—
S	2400⋯3700	ZiO & LaO
R	3700 ⋯ 5200	Carbon rich
N	2400⋯3700	Carbon rick
WN or W-N	28k ⋯ 50k	He& N Wolf-Rayet
WC or W-C	28k ⋯ 50k	He, C, & O Wolf-Rayet
WR or W-R	25k ⋯ 50k	general Wolf-Rayet
X	?	X-Ray source
D	varies	remnant cores of non-

Note:

• various sources disagree on the exact temperatures for types O, G, K, & M, and types L are sometimes given M with subclassifications 10-19... I have gone with the outer range listed across various sources.
• The IAU has yet to formally approve types L/T/Y, but their membership is using them anyway.
• Class X includes active neutron stars, pulsars, and black holes.
• Morgan-Keenan only included OBAFGKM,
• Certain 1960's & 70's sources included type N and S in the places now used for L & T. I've found no non-american sources doing so.
• Types S & N are used for different types of stars otherwise like type M but with major metalicity type differences
• type R is to type K as N is to M.
• WR, WC, and WN are thought to be exposed cores of type O stars. They're expected to be on course for type Ⅰb or Ⅰc
• The size roman numerals are the Yerkes system, running Ⅰa, Ⅰb, Ⅱ, Ⅲ, Ⅳ , Ⅴ (ofted said as Dwarf rarely coded as D), Ⅵ or SD, Ⅶ or WD or .
  • A few odd items were coded as Ⅷ... but that wasn't formally part of the Yerkes system. That would fit well for larger brown dwarves - L0 to L5, which are potentially fusing Deuterium and tritium in their cores, but not Protium.
  • Theoretically, someone mentioned Class Ⅸ as sub-fusion brown dwarves. Classes Ⅷ and beyond would all be infrared peak output, and be dim violet to dim red in visual colors...

Which leaves

• nonignition nebulae (stellar mass clouds without yet having a brown-dwarf or larger central mass)
• rogue sub-brown-dwarf planets - smallest detected is estimated to be subterran mass.
• non-active neutron stars (some have residual temps sufficient for a spectral type),
• Black Dwarfs (which should not yet exist, save as artifacts from sub-stability mass primordial black holes),
• icy bodies of any size below 200 Kelvins surface temp,
• indirectly discovered massive objects (invisible companions of visible items causing detectable spectral wobble) including PlaneMOs...
• Items with bizarre spectral characteristics
  • binaries which cannot be resolved sufficient for separately spectral classification. These are not uncommon; modern spectroscopy can usually make pretty good guesses, tho'
  • Items too cold/cold for a known mass and composition.
  • Items too hot/cold, red/blue, for their absolute magnitude (A triple brightness type M could be a close trinary of three type M stars, for example.) and motion... but until it can be resolved, it's outside the diagnostics for type M. A dim M-spectrum could be being observed through clouds of debris.

Anyway, 11k systems would then fit into ³√(¾·11k·17.28/π) = 35.7 pc radius

Assuming that the 3I actually operates in 3D volumetric space. Marc had me do all the jump interaction math with the interceptions and blockage for J-space being a wavy sheet across N-space. This is probably for simple gamist reasons... playability, but it was direct instruction from Marc. (That math is also why the increasing exclusion radii of S/H/L/B/V drives got dropped; specifically, that was what I and Cryton were checking for Marc. A B1 would never be able to get a full B1 within the galactic plane. And that's based upon the 2010 available stellar catalogs.)

THen again, the number of bodies detected within 50 LY more than trebled since 2010 (when it was about 500 known) to over 1500 now... heck, the shell between 55 and 60 LY has nearly 100 entries, many of which are binaries/trinaries, about 5 of which are class T and 10 class L. On a quick skim, at least.

Y-type star

https://www.atnf.csiro.au/outreach/... have the,zirconium oxide and lanthanum oxide. http://astro.wku.edu/astr106/stella...The R and N classifications,N stars to type M.

https://sites.uni.edu/morgans/astro/course/Notes/section2/spectraltemps.html

https://sites.uni.edu/morgans/astro/course/Notes/section2/spectraltemps.html

The masses of Wolf-rayet stars.

The masses, mass ratios, and orbital parameters of Wolf-Rayet binaries are discussed. There is no one typical mass for W-R stars, since the known masses range from 10 to 50 solar masses, and span a much larger range in mass than do their O type companions. The average mass of a W-R star is about...

ui.adsabs.harvard.edu

https://astronomy.swin.edu.au/cosmos/w/wolf-rayet+star https://winknews.com/2020/10/30/astronomers-find-smallest-rogue-planet-in-the-milky-way

Astronomers find smallest 'rogue planet' in the Milky Way

Astronomers have detected the smallest rogue planet in our Milky Way galaxy, and it’s between the sizes of Mars and Earth. Rogue planets are free-floating planets that don’t orbit stars. The planet, named OGLE-2016-BLG-1928, was found by astronomers using the Warsaw Telescope at Las Campanas...

winknews.com

 

[Timerover51]

So no more Oh Be A Fine Girl Kiss Me? I have to come up with L T Y?

 

[Spinward Flow]

So no more Oh Be A Fine Girl Kiss Me? I have to come up with L T Y?

Oh
Be
A
Fine
Girl
Kiss
Me
Lips
Tongue
Yay

 

[Straybow]

Assuming that the 3I actually operates in 3D volumetric space. Marc had me do all the jump interaction math with the interceptions and blockage for J-space being a wavy sheet across N-space. This is probably for simple gamist reasons... playability, but it was direct instruction from Marc. (That math is also why the increasing exclusion radii of S/H/L/B/V drives got dropped; specifically, that was what I and Cryton were checking for Marc. A B1 would never be able to get a full B1 within the galactic plane. And that's based upon the 2010 available stellar catalogs.)

I have no idea what you're talking about, nor what it has to do with putting a 3I sized polity in 3D space instead of a pencil-and-paper friendly planar game map. S/H/L/B/V?

 

[Spinward Flow]

I have no idea what you're talking about, nor what it has to do with putting a 3I sized polity in 3D space instead of a pencil-and-paper friendly planar game map. S/H/L/B/V?

It's astronomy.
It's not meant to be understood ...
It's an ART, not a SCIENCE ... ... just smile and nod appreciatively and we'll all get along SPLENDIDLY!

"Move along, move along ... no awesomely powerful self-regulating fusion reactors anywhere near here. Move along, move along ..."

 

[whulorigan]

I have no idea what you're talking about, nor what it has to do with putting a 3I sized polity in 3D space instead of a pencil-and-paper friendly planar game map. S/H/L/B/V?

From T5 (Higher Order Drives):
J = Jump (100 D limit)
H = Hop (1000 D limit)
S = Skip (10,000 D limit)
L = Leap (100,000 D limit)
B = Bound (1,000,000 D limit)
V = Vault (10,000,000 D limit)

Each is an order of magnitude greater travel distance per week per number-rating then the previous order Drive system.

But the Higher Order magnitude drive systems were conceived of as having a correspondingly higher order of magnitude jump exclusion/shadow as well. When Aramis (et al) ran the numbers, they discovered that the Higher Order Drives in 3D (if allowed to have the higher order of magnitude jump exclusion shadow) would effectively become useless due to galactic stellar density.

 

[mike wightman]

But could be used to travel between galaxies...

 

[Spinward Flow]

But could be used to travel between galaxies...

But what about the Energy Barrier at the edge of the galaxy?

 

[whulorigan]

But what about the Energy Barrier at the edge of the galaxy?

Hasn't been a problem since they figured out how to mix matter and antimatter cold . . .

 

[Krikkitone]

From T5 (Higher Order Drives):
J = Jump (100 D limit)
H = Hop (1000 D limit)
S = Skip (10,000 D limit)
L = Leap (100,000 D limit)
B = Bound (1,000,000 D limit)
V = Vault (10,000,000 D limit)

Each is an order of magnitude greater travel distance per week per number-rating then the previous order Drive system.

But the Higher Order magnitude drive systems were conceived of as having a correspondingly higher order of magnitude jump exclusion/shadow as well. When Aramis (et al) ran the numbers, they discovered that the Higher Order Drives in 3D (if allowed to have the higher order of magnitude jump exclusion shadow) would effectively become useless due to galactic stellar density.

Although you would just use lower order drives to hop around the galaxy, and higher order ones to hop between galaxies.

You don’t have serious problems until you get to Vault drives (Sol excludes 100,000AU ie half a parsec)…. but a Vault drive takes you ~ 3x the total diameter of the milky way.

 

[mike wightman]

Someone would eventually invent a hybrid drive - it can operate as a jump, hop, skip

 

[Krikkitone]

Someone would eventually invent a hybrid drive - it can operate as a jump, hop, skip

Even without a hybrid, the ship just has multiple drives
Maneuver… get past 100D
Jump….get past ~100 AU/1000 AU from star
Skip/Leap….skip a few hundred/thousand parsecs up or down to be out of the galactic plane
Bound/Vault6,7,8,9 drive….. takes you across the galaxy/to new galaxies

then reverse to get back to a planet

4 different drives needed…up from 2 in 3I

(although you could have ships that specialized…ie Vault+Maneuver ships that only travelled between extragalactic starports…which are connected into the galactic plane with Leap ships that ferry passengers and cargo to Oort cloud bases… where “jump shuttles” get you to the planet.)

 

[whulorigan]

Even without a hybrid, the ship just has multiple drives
Maneuver… get past 100D
Jump….get past ~100 AU/1000 AU from star
Skip/Leap….skip a few hundred/thousand parsecs up or down to be out of the galactic plane
Bound/Vault6,7,8,9 drive….. takes you across the galaxy/to new galaxies

then reverse to get back to a planet

4 different drives needed…up from 2 in 3I

(although you could have ships that specialized…ie Vault+Maneuver ships that only travelled between extragalactic starports…which are connected into the galactic plane with Leap ships that ferry passengers and cargo to Oort cloud bases… where “jump shuttles” get you to the planet.)

Yes, but you also have to take into account "scatter" at the destination point, which is the increasing uncertainty of the actual emergence point relative to the desired emergence point with increasing drive order, if there is an astrogation failure (and for higher order drives, there usually is). With Hop and Jump it is only on the order of ± ~100,000 km or so. But the higher order drives can have scatter on the order of multiple parsecs or a sector or more.

 

[Spinward Flow]

Yes, but you also have to take into account "scatter" at the destination point, which is the increasing uncertainty of the actual emergence point relative to the desired emergence point with increasing drive order, if there is an astrogation failure (and for higher order drives, there usually is). With Hop and Jump it is only on the order of ± ~100,000 km or so. But the higher order drives can have scatter on the order of multiple parsecs or a sector or more.

Get thee better computers and software, young man.