Milky Way

This article is about the galaxy. For other uses, see Milky Way (disambiguation).

Milky Way
The Galactic Center as seen from Earth's night sky (featuring the telescope's laser guide star). Listed below is Galactic Center's information.
Observation data (J2000 epoch)
ConstellationSagittarius
Right ascension17h 45m 40.03599s[1]
Declination−29° 00′ 28.1699″[1]
Distance7.935–8.277 kpc (25,881–26,996 ly)[2][3][4][a]
Characteristics
TypeSb; Sbc; SB(rs)bc[5][6]
Mass1.15×1012[7][8][9] M☉
Number of stars100–400 billion ((1–4)×1011)[12][13]
Size26.8 ± 1.1 kpc (87,400 ± 3,600 ly)
(diameter; D25 isophote)[10][b]
Thickness of thin disk220–450 pc (718–1,470 ly)[14]
Thickness of thick disk2.6 ± 0.5 kpc (8,500 ± 1,600 ly)[14]
Angular momentum~1×1067 J s[15]
Sun's Galactic rotation period212 Myr[16]
Spiral pattern rotation period220–360 Myr[17]
Bar pattern rotation period160–180 Myr[18]
Speed relative to CMB rest frame552.2±5.5 km/s[19]
Escape velocity at Sun's position550 km/s[20]
Dark matter density at Sun's position0.0088+0.0024
−0.0018 M☉pc−3 (0.35+0.08
−0.07 GeV cm−3)[20]
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The Milky Way[c] is the galaxy that includes the Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye.

The Milky Way is a barred spiral galaxy with a D25 isophotal diameter estimated at 26.8 ± 1.1 kiloparsecs (87,400 ± 3,600 light-years),[10] but only about 1,000 light-years thick at the spiral arms (more at the bulge). Recent simulations suggest that a dark matter area, also containing some visible stars, may extend up to a diameter of almost 2 million light-years (613 kpc).[26][27] The Milky Way has several satellite galaxies and is part of the Local Group of galaxies, which form part of the Virgo Supercluster, which is itself a component of the Laniakea Supercluster.[28][29]

It is estimated to contain 100–400 billion stars[30][31] and at least that number of planets.[32][33] The Solar System is located at a radius of about 27,000 light-years (8.3 kpc) from the Galactic Center,[34] on the inner edge of the Orion Arm, one of the spiral-shaped concentrations of gas and dust. The stars in the innermost 10,000 light-years form a bulge and one or more bars that radiate from the bulge. The Galactic Center is an intense radio source known as Sagittarius A*, a supermassive black hole of 4.100 (± 0.034) million solar masses.[35][36] The oldest stars in the Milky Way are nearly as old as the Universe itself and thus probably formed shortly after the Dark Ages of the Big Bang.[37]

Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. Until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe.[38] Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Doust Curtis,[39] observations by Edwin Hubble showed that the Milky Way is just one of many galaxies.

  1. ^ a b Petrov, L.; Kovalev, Y. Y.; Fomalont, E. B.; Gordon, D. (2011). "The Very Long Baseline Array Galactic Plane Survey—VGaPS". The Astronomical Journal. 142 (2): 35. arXiv:1101.1460. Bibcode:2011AJ....142...35P. doi:10.1088/0004-6256/142/2/35. ISSN 0004-6256. S2CID 121762178.
  2. ^ Event Horizon Telescope Collaboration; et al. (2022). "First Sagittarius A* Event Horizon Telescope Results. VI. Testing the Black Hole Metric". The Astrophysical Journal. 930 (2): L17. arXiv:2311.09484. Bibcode:2022ApJ...930L..17E. doi:10.3847/2041-8213/ac6756. S2CID 248744741.
  3. ^ Banerjee, Indrani; Sau, Subhadip; SenGupta, Soumitra (2022). "Do shadows of SGR A* and M87* indicate black holes with a magnetic monopole charge?". arXiv:2207.06034 [gr-qc].
  4. ^ Abuter, R.; et al. (2019). "A geometric distance measurement to the Galactic center black hole with 0.3% uncertainty". Astronomy & Astrophysics. 625: L10. arXiv:1904.05721. Bibcode:2019A&A...625L..10G. doi:10.1051/0004-6361/201935656. S2CID 119190574.
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  6. ^ Frommert, Hartmut; Kronberg, Christine (August 26, 2005). "Classification of the Milky Way Galaxy". SEDS. Archived from the original on May 31, 2015. Retrieved May 30, 2015.
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  14. ^ a b Bland-Hawthorn, Joss; Gerhard, Ortwin (2016). "The Galaxy in Context: Structural, Kinematic, and Integrated Properties". Annual Review of Astronomy and Astrophysics. 54: 529–596. arXiv:1602.07702. Bibcode:2016ARA&A..54..529B. doi:10.1146/annurev-astro-081915-023441. S2CID 53649594.
  15. ^ Karachentsev, Igor. "Double Galaxies § 7.1". ned.ipac.caltech.edu. Izdatel'stvo Nauka. Archived from the original on March 4, 2016. Retrieved April 5, 2015.
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  18. ^ Shen, Juntai; Zheng, Xing-Wu (2020). "The bar and spiral arms in the Milky Way: Structure and kinematics". Research in Astronomy and Astrophysics. 20 (10): 159. arXiv:2012.10130. Bibcode:2020RAA....20..159S. doi:10.1088/1674-4527/20/10/159. S2CID 229005996.
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  21. ^ Laustsen, Svend; Madsen, Claus; West, Richard M. (1987). Exploring the Southern Sky: a Pictorial Atlas from the European Southern Observatory (ESO). Berlin, Heidelberg: Springer. p. 119. ISBN 978-3-642-61588-7. OCLC 851764943.
  22. ^ Pasachoff, Jay M. (1994). Astronomy: From the Earth to the Universe. Harcourt School. p. 500. ISBN 978-0-03-001667-7.
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  35. ^ Overbye, Dennis (January 31, 2022). "An Electrifying View of the Heart of the Milky Way – A new radio-wave image of the center of our galaxy reveals all the forms of frenzy that a hundred million or so stars can get up to". The New York Times. Archived from the original on January 31, 2022. Retrieved February 1, 2022.
  36. ^ Heyood, I.; et al. (January 28, 2022). "The 1.28 GHz MeerKAT Galactic Center Mosaic". The Astrophysical Journal. 925 (2): 165. arXiv:2201.10541. Bibcode:2022ApJ...925..165H. doi:10.3847/1538-4357/ac449a. S2CID 246275657.
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