Galactic halo

A galactic halo is an extended, roughly spherical component of a galaxy which extends beyond the main, visible component.^[1] Several distinct components of a galaxy comprise its halo:^[2]^[3]

the stellar halo
the galactic corona (hot gas, i.e. a plasma)
the dark matter halo

The distinction between the halo and the main body of the galaxy is clearest in spiral galaxies, where the spherical shape of the halo contrasts with the flat disc. In an elliptical galaxy, there is no sharp transition between the other components of the galaxy and the halo.

A halo can be studied by observing its effect on the passage of light from distant bright objects like quasars that are in line of sight beyond the galaxy in question.^[4]

^ "OpenStax Astronomy". OpenStax.
^ Helmi, Amina (June 2008). "The stellar halo of the Galaxy". The Astronomy and Astrophysics Review. 15 (3): 145–188. arXiv:0804.0019. Bibcode:2008A&ARv..15..145H. doi:10.1007/s00159-008-0009-6. ISSN 0935-4956. S2CID 2137586.
^ Maoz, Dan (2016). Astrophysics in a Nutshell. Princeton University Press. ISBN 978-0-691-16479-3.
^ August 2020, Meghan Bartels 31 (31 August 2020). "The Andromeda galaxy's halo is even more massive than scientists expected, Hubble telescope reveals". Space.com. Retrieved 2020-09-01.{{cite web}}: CS1 maint: numeric names: authors list (link)

[1] "OpenStax Astronomy". OpenStax.

[2] Helmi, Amina (June 2008). "The stellar halo of the Galaxy". The Astronomy and Astrophysics Review. 15 (3): 145–188. arXiv:0804.0019. Bibcode:2008A&ARv..15..145H. doi:10.1007/s00159-008-0009-6. ISSN 0935-4956. S2CID 2137586.

[3] Maoz, Dan (2016). Astrophysics in a Nutshell. Princeton University Press. ISBN 978-0-691-16479-3.

[4] August 2020, Meghan Bartels 31 (31 August 2020). "The Andromeda galaxy's halo is even more massive than scientists expected, Hubble telescope reveals". Space.com. Retrieved 2020-09-01.{{cite web}}: CS1 maint: numeric names: authors list (link)

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