Thick disk

It was shown that there is a diversity of thick disc formation scenarios.^[8] In general, various scenarios for the formation of this structure have been proposed, including:

• Thick disks come from the heating of the thin disk^[9][10]
• It is a result of a merger event between the Milky Way and a massive dwarf galaxy^[3]
• More energetic stars migrate outwards from the inner galaxy to form a thick disk at larger radii^[11][12]
• The disk forms thick at high redshift with the thin disk forming later^[13][14]
• Disk flaring combined with inside-out disk formation^[15][16]
• Scattering by massive clumps: stars born in massive gas clumps tend to be scattered to a thick disc and to be enriched in alpha-elements, while those formed out of these clumps form a thin disc and are alpha-poor^[17][18][19]

Although the thick disk is mentioned as a bona fide galactic structure in numerous scientific studies and it's even thought to be a common component of disk galaxies in general,^[20] its nature is still under dispute.

The view of the thick disk as a single separate component has been questioned by a series of papers that describe the galactic disk with a continuous spectrum of components with different thicknesses.^[21][22]

• Disk galaxy
• Galactic coordinate system
• Galaxy formation and evolution

Galaxy parts

• Galactic bulge
• Galactic halo
• Spiral arm
• Thin disk

• Thin and Thick Galactic Disks
• Structure and Evolution of the Milky Way
• Populations & Components of the Milky Way