Caption: A cartoon of the Milky Way (AKA the Galaxy)---which is a fairly typical spiral galaxy. Note that the values in the cartoon are somewhat out of date, but are still good enough roughly speaking. Note also that since Milky Way structures have NO sharp edges, sizes are somewhat dependent on the definition used by those assigning the size.

Features:

1. The main components of the Milky Way in outward going order roughly speaking: Sagittarius A* (Galactic central black hole, Milky Way or Galactic center black hole), Milky Way center (AKA Galactic center of mass): distance = 8.122(31) kpc = 26.490(100) kly, Milky Way bulge: radius ∼ 3 kpc, Milky Way bar, Milky Way disk (Milky Way: disk diameter ≅ 30 kpc, disk average thickness ≅ 0.3 kpc), Milky Way spiral arms, Milky Way globular clusters (more than 150 are known: see Wikipedia: Globular clusters; Wikipedia: List of globular clusters), Milky Way halo: stellar matter radius ∼ 60 kpc, Milky Way dark matter halo: radius >∼ 100 kpc ???, Milky Way mass: total/dark matter ∼ 10**12 M_☉, stars/gas/dust ∼ 5*10**10 M_☉ ≅ 5 % of total.

2. Overwhelmingly most spiral galaxies have obvious galactic bulges and galactic disks: Milky Way is typical of this. However, they all have rather spherical galactic halos (which consist of low-density baryonic matter (interstellar medium (ISM), rather isolated stars, and globular clusters) and dark matter). The galactic halos can extend much farther than the galactic disks, but their edges are hard to find since they become invisible as the baryonic matter gets rarer going outward. The distribution and extent of dark matter in the dark matter halos is particularly hard to determine since it is entirely invisible so far, except through the effects of its gravity. The dark matter halos (probably rather spherical in general) may extend out to >∼ 100 kpc from the spiral galaxy center and have ∼ 5 -- 20 times ???? the mass of all the baryonic matter in the spiral galaxy. Computer simulations based on the Λ-CDM model give some insight into the structure of dark matter halos insofar as they are realistic.

   Stellar streams (made of tidally disrupted dwarf galaxies or globular clusters) in the Milky Way may eventually give direct observational information about the distribution of dark matter in Milky Way dark matter halo (see Eric Hand, Science, 2018oct05, "Sky Rivers").

3. See Keywords: Milky Way below or at keywords_milky_way.html:
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4. References: Cox-570, CK-379, FK-556,566, Shu-257.