Milky Way Galaxy

Galaxias (Milky Way Galaxy)
Charted Space depicted with rimward Orion Spur from Sagittarius-Carina Arm

The Milky Way Galaxy (otherwise known as Galaxias or Dakhaseri) is the name given to the SB(bc)-type barred-spiral galaxy in which the stars of Charted Space reside. It is but one of the 2 trillion galaxies in the observable universe.

Description[edit]

Galaxias is approximately 30 kiloparsecs in diameter and is estimated to be between 300 and 600 parsecs thick in the region of the galactic disk, thickening to at least 1,000 to 1,500 parsecs toward the galactic center. The density of stars generally drops off exponentially with distance both in the direction of the galactic core to the galactic rim, as well as in thickness from the mean galactic plane to the outer surfaces of the disk. Approximately 95% of the disk stars lie within the 300pc thick region of the disk.

While Galaxias is almost as old as the universe itself (its oldest stars date to less than a billion years after the beginning of time), the majority of its stars are middle-aged and range between 6 and 10 billion years of age, and number between 200 to 400 billion star systems in total. Most of its stars have planetary systems with habitable zones capable of producing and supporting life.

Galactic Anatomy[edit]

Galaxias can be divided into three primary regions: the dense Galactic Core composed of closely packed old stars, the Galactic Disc containing a continuously decreasing-with-radius lower-density distribution of older, cooler stars interspersed with luminous spiral-shaped regions of higher density dust and gas where new star formation is actively ongoing, and the Galactic Halo, a sparsely-populated spherical region englobing the entire structure containing occasional dense Globular Clusters of old red stars orbiting the Galactic Core in orbits of both varying ellipticity and angle to the galactic disc, about 40% of which are retrograde orbits.

Galactic Core[edit]

The stars within the central 1500 pc radius form a spheroidal bulge and one or more "bars" that radiate from the bulge. These elongated bar-shaped structures have a stellar density of over 50,000 stars per cubic parsec. At the very center of the core of Galaxias is a super-massive black hole named Sagittarius A* that masses approximately 4.3 x 10⁶ M_Sol. Approximately 10 million stars orbit within 1.0 lightyear of this object.

Galactic Disc[edit]

As a Spiral Galaxy subtype, outside of the Galactic Core the primary stellar distribution of Galaxias lies within a roughly (uneven) planar disc of mostly older "redder" (Type G thru M) stars and stellar remnants. Within this disc, regions of higher densities of Molecular Hydrogen, dust and gas have become "compressed" as a result of rotation about the central galactic black hole and the gravitational influence of dark matter, causing more recent star formation (and the appearance of stellar types of all classifications, O thru M) to occur just behind these density-compression wavefronts. As these star-forming regions contain short-lived, young, "bright" and "hot" stars, they stand out from the dimmer and cooler background stars and trace out the pattern of these compression regions as they continue to rotate, the individual stars moving about their independent orbits about the galactic center and forming an optical spiral pattern against the backdrop.

These spiral patterns, or "spiral arms" are typically "named" based on the night-sky constellation in which they were first observed and identified on Ancient Terra. As these arms continue to wind about Galaxias, they eventually appear to move out of their initial "constellation" of first-identification and may have arm-sections that become renamed (or not), based more on tradition than rule. As a result, some arms or sections of arms can bear multiple historical names, especially if better future observations more clearly identified the actual arm-structure in a more particular specified fashion.

Based on observations, Galaxias appears to have two "major" (higher-density) spiral arms as traced by old stars:

The Perseus Arm, which may be an extension of the 3kpc Arm on the Far Side
The Scutum-Crux Arm (aka the "Centaurus Arm" or "Scutum-Centaurus Arm" eventually becoming simply the "Scutum Arm" on the Far Side)

Galaxias also appears to have four "minor" (lower-density) spiral arms as traced by gas and both old and young stars:

The Norma Arm, a coreward branch off the "Centaurus Arm" which becomes the Cygnus-Outer Arm and New/Norma-Outer Arm further along (sometimes simply known as the "Cygnus-Norma Outer Arm" or simply the "Outer Arm")
The Sagittarius Arm (which becomes the Sagittarius-Carina Arm farther along on the Near Side of Galaxias
The Orion Arm (aka the "Cygnus-Orion Spur") which branches from the Sagittarius Arm
The 3kpc Arm surrounding the Near and Far Side of the Galactic Core).

Altogether outside of the spiral arms and beyond them is a coplanar stellar stream known as the Monoceros Ring (or Outer Ring), a ring of gas and stars torn from other galaxies billions of years ago. Galaxias's stellar disk does not have a sharp edge beyond which there are no stars; rather, the concentration of stars decreases exponentially with distance from the center of Galaxias. For reasons that are not understood, beyond a radius of roughly 13 kpc from the center, the number of stars per cubic parsec drops much faster with radius.

Sol System and Charted Space[edit]

Map combining both concepts: The "Rimward Spur" of the more coreward arm joins further to spinward with the Perseus Arm, of which it is a coreward branch.

The Sol Star System within Charted Space is located within the galactic disk, about 8,150 pc from the Galactic Center, on the inner edge of one of the spiral-shaped concentrations of gas and dust called the "Local Arm" or "Orion Arm" (or occasionally the "Orion-Cygnus Spur" of the Sagittarius-Carina Arm) ^*, about 6pc North of the mean galactic plane. ^[1]

^* Scientists currently debate as to whether the Local Region of Charted Space lies along the inner (coreward) edge of a rimward Spur of the Sagittarius-Carina Arm known as the Orion Spur, or whether the Local Region is actually a more substantive minor arm of its own (the Orion Arm) that is a coreward split from the Perseus Arm to rimward.

The spaces between the galactic arms are somewhat less dense in stars, but have comparatively less gas and dust than the spiral arms themselves, and are thus not generally regions of active star formation. As a result, most stars here tend to be cooler older stars and stellar remnants. The spiral arms themselves are thus largely an "optical" phenomenon, as the abundance of very young hot bright stars in the star-forming regions of the "arms" causes these regions to "stand out" visually compared to the regions populated by older and cooler stars that permeate the majority of the galactic disk.

Galactic Halo[edit]

Surrounding the galactic disk is a sparse spherical Galactic Halo of old stars and globular clusters that extends further than the galactic disk but is limited in size by the orbits of Galaxias's two satellite galaxies, the Large and Small Magellanic Clouds. Approximately 90% of globular clusters lie within 30 kpc of the Galactic Center, of which 40% are on retrograde orbits relative to the rotation of the galactic disk.

Stellar Streams[edit]

Galaxias is also encircled by several Stellar Streams, which are associations of stars orbiting Galaxias (and other galaxies as well) that were likely once Globular Clusters or Dwarf Galaxies that were torn apart and stretched out along their orbits by tidal forces.

Galaxias has well over 20 known Stellar Streams.

Satellite Galaxies & Galactic Neighborhood[edit]

See list at Universe

Galaxias has a number of Satellite Galaxies (including the Large and Small Magellanic Clouds, the Sagittarius Dwarf Galaxy the Virgo Stellar Stream, and the Canis Major Dwarf Galaxy) and is part of a cluster of galaxies known as the Local Group, which is itself a component of the Virgo Supercluster, which is a component of the Laniakea Supercluster. Galaxias is the second largest galaxy in the Local Group, the Andromeda Galaxy (M31) being larger.

Galactic Mapping and Coordinates[edit]

Positions of objects in Galaxias are specified by six primary directions nominally labelled Coreward (toward the galactic core), Rimward (diametrically opposite the direction of the galactic core), Spinward (in the direction of galactic rotation), Trailing (opposite the direction of galactic rotation), North (above the galactic plane), and South (below the galactic plane).

Modern Imperial astrogational coordinates and directions within Galaxias are specified both by the latitudinal distance from the galactic core ("ring") and longitudinal angle ("ray") from a meridian that extends from the galactic core through a reference point defined by the central star of the star system known as Reference (aka "Aadkhien"). Orthogonal projections above/below the galactic plane intersecting "Aadkhien Primary" at Reference are further specified as necessary. Essentially, Reference is by definition assigned, Ring=10,000.0/Ray= 000.0° ("First Ray") meaning that each 1.0 pc astrogational hexgrid is approximately 1 ring linear or 1 ray angular displacement at Charted Space range. Please see Galactic Directions and the appropriate section in the article Astrography for details.

The old Solomani system of spherical galactic coordinates is based on a meridian-line running between the star Sol and Sagittarius A*, with Sol at the origin of the coordinate system. Due Coreward is defined as bearing 000^o longitude, due Spinward is defined as bearing 090^o longitude, due Rimward is defined as bearing 180^o longitude, and due Trailing is defined as bearing 270^o longitude. Spherical coordinate latitude angles are defined as a bearing angle +/- 90^o above (i.e. North of) or below (i.e. South of) the galactic plane. The region from 000° to 090° defines Galactic Quadrant I, the region from 090° to 180° defines Galactic Quadrant II, the region from 180° to 270° defines Galactic Quadrant III, and the region from 270° to 000° defines Galactic Quadrant IV. These can be subdivided into North or South Octant, respectively.

History[edit]

Galaxias is home to Humaniti and hundreds, perhaps thousands, of other sapient non-human species. In some of Galaxias's systems, life has come and gone, and their worlds bear the marks of long-dead civilizations. In other systems, life has not yet arisen, though some day it may. But in many systems, worlds have produced intelligent life, known as NILs, with cultures and societies almost too strange to understand.

Extra-Galactic Sophonts[edit]

The following sophont species are rumored to have had their origin in a galaxy other than Galaxias, but the truth of these claims, and the likely galaxy of origin are matters of mere speculation.

Bolth - Zachrisson/Fulani ^[2]

Vilani Galaxy Appellation[edit]

The Vilani name for the Milky Way Galaxy is Dakhaseri, after an ancient Vilani story that tells of meritorious souls allowed to watch the events of the world; their discussions (and futile attempts to intervene) are the basis of many Vilani myths.

Image Repository[edit]

TravellerMap (T5SS):
[1]

Sources[edit]

This article has a secret.

This page uses content from Wikipedia. The original article was at Milky_Way. The list of authors can be seen in the page history. The text of Wikipedia is available under the Commons Attribution-ShareAlike 3.0 Unported License.

This list of sources was used by the Traveller Wiki Editorial Team and individual contributors to compose this article. Copyrighted material is used under license from Mongoose Publishing or by permission of the author. The page history lists all of the contributions.

Chuck Kallenbach. Vanguard Reaches (Paranoia Press, 1981), TBD.
Marc Miller. T5 Core Rules (Far Future Enterprises, 2013), 14. (T5.09, pg.14) (T5.10, Book 1, pg.10)
Traveller Map: [2]
"Scientific American" [3]. "New View of the Milky Way" (April 2020). p. 35
Author & Contributor: WHULorigan

↑ Scientific American (April 2020), p. 35
↑ Chuck Kallenbach. Vanguard Reaches (Paranoia Press, 1981), 11.

[1] Scientific American (April 2020), p. 35

[2] Chuck Kallenbach. Vanguard Reaches (Paranoia Press, 1981), 11.

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