thin disk

{{Short description|Structural component of galaxies}}

File:Milky-way-edge-on.pdf

The thin disk is a structural component of spiral and S0-type galaxies, composed of stars, gas and dust. It is the main non-centre (e.g. galactic bulge) density of such matter. That of the Milky Way is thought to have a scale height of around {{Nowrap|{{convert|300-400|pc|lk=on}}}} in the vertical axis perpendicular to the disk,Bradley W. Carroll and Dale A. Ostlie, 2007, "An Introduction to Modern Astrophysics" Second Edition and a scale length of around {{Nowrap|{{convert|2.5-4.5|kpc|lk=on}}}} in the horizontal axis, in the direction of the radius.{{cite book|title=Galaxies in the universe : an introduction|date=2007|publisher=Cambridge Univ. Press|isbn=978-0521671866|edition=2.|location=Cambridge|last1=Sparke|first1=Linda S.|author1-link=Linda Sparke|last2=Gallagher|first2= John S. III}} For comparison, the Sun is {{Nowrap|{{convert|8|kpc|lk=on}}}} out from the center. The thin disk contributes about 85% of the stars in the Galactic plane{{cite journal | arxiv=0911.3598| title=The Stellar Population of the Thin Disk | author=Carlos Allende Prieto | journal=Proceedings IAU Symposium | volume=265 |date=Nov 2009 | issue=265| pages=304–312 |bibcode = 2010IAUS..265..304A |doi = 10.1017/S1743921310000785 | s2cid=118520855 }} and 95% of the total disk stars. It can be set apart from the thick disk of a galaxy since the latter is composed of older population stars created at an earlier stage of the galaxy formation and thus has fewer heavy elements. Stars in the thin disk, on the other hand, are created as a result of gas accretion at the later stages of a galaxy formation and are on average more metal-rich.{{cite web|title=OpenStax CNX|url=https://cnx.org/contents/LnN76Opl@10.13:-E7ILRpl@3/The-Formation-of-the-Galaxy|website=cnx.org|access-date=31 January 2017}}

The thin disk contains stars with a wide range of ages and may be divided into a series of sub-populations of increasing age. Notwithstanding, it is considered to be considerably younger than the thick disk.Bensby & Feltzing, "The Galactic thin and thick discs in the context of galaxy formation", {{ArXiv|0908.3807}}

Based upon the emerging science of nucleocosmochronology, the Galactic thin disk of the Milky Way is estimated to have been formed 8.8 ± 1.7 billion years ago.Eduardo F. del Peloso a1a, Licio da Silva a1, Gustavo F. Porto de Mello and Lilia I. Arany-Prado (2005), "The age of the Galactic thin disk from Th/Eu nucleocosmochronology: extended sample" (Proceedings of the International Astronomical Union (2005), 1: 485-486 Cambridge University Press) It may have collided with a smaller satellite galaxy, causing the stars in the thin disk to be shaken up and creating the thick disk,

{{cite journal

|last=Kasparova |first=A.

|year=2016

|title=The Diversity of Thick Galactic Discs

|journal=Monthly Notices of the Royal Astronomical Society: Letters

|volume=460 |issue=1 |pages=89–93

|arxiv=1604.07624

|bibcode=2016MNRAS.460L..89K

|doi=10.1093/mnrasl/slw083

|doi-access=free

}} while the gas would have settled into the galactic plane and reformed the thin disk.