= Solution
The <Milky Way> has a thin stellar <galactic disk>, radius roughly $15$–$20\,\mathrm{kpc}$ and scale height about $0.3\,\mathrm{kpc}$, containing gas, dust, young and old stars, <spiral arms> and most current <star formation>. Its stellar mass is a few $10^{10}M_\odot$. A thicker, older <galactic disk> has scale height around $1\,\mathrm{kpc}$ and stellar mass of order $10^{10}M_\odot$, with little cold gas.
The central <galactic bulge> and bar extend a few thousand <parsecs> and contain about $10^{10}M_\odot$, largely older stars. The central <supermassive black hole> has mass about $4\times10^6M_\odot$ and is negligible in the total galactic budget. A diffuse old metal-poor <stellar halo>, extending tens to over $100\,\mathrm{kpc}$, contains <globular clusters> and roughly $10^9M_\odot$ in stars. An extended <dark matter halo> reaches roughly $200\,\mathrm{kpc}$ and dominates the total mass, of order $10^{12}M_\odot$. These are approximate component scales; the gaseous <galactic halo> also extends beyond the stellar <galactic disk>.
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