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Andromeda Galaxy ❍｜Definition｜1st｜20260324231633-00-⌔

Andromeda Galaxy - Wikipedia

Andromeda Galaxy

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The Andromeda Galaxy is a barred spiral galaxy¹ and is the nearest major galaxy to the Milky Way. It was originally named the Andromeda Nebula and is cataloged as Messier 31, M31, and NGC 224. Andromeda has a D${}_{25}$ isophotal diameter of about 46.56 kiloparsecs (152,000 light-years)[^10] and is approximately 765 kpc (2.5 million light-years) from Earth. The galaxy’s name stems from the area of Earth’s sky in which it appears, the constellation of Andromeda, which itself is named after the princess who was the wife of Perseus in Greek mythology.[

The virial mass of the Andromeda Galaxy is of the same order of magnitude as that of the Milky Way, at 1 trillion solar masses (2.0 × 10${}^{42}$ kilograms). The mass of either galaxy is difficult to estimate with any accuracy, but it was long thought that the Andromeda Galaxy was more massive than the Milky Way by a margin of some 25% to 50%.² However, this has been called into question by early-21st-century studies indicating a possibly lower mass for the Andromeda Galaxy² and a higher mass for the Milky Way.³⁴ The Andromeda Galaxy has a diameter of about 46.56 kpc (152,000 ly), making it the largest member of the Local Group of galaxies in terms of extension.⁴

The Milky Way and Andromeda galaxies have about a 50% chance of colliding with each other in the next 10 billion years,⁵ merging to potentially form a giant elliptical galaxy⁶ or a large lenticular galaxy.⁷

With an apparent magnitude of 3.4, the Andromeda Galaxy is among the brightest of the Messier objects,⁸ and is visible to the naked eye from Earth on moonless nights,⁹ even when viewed from areas with moderate light pollution.[

Printed 2026-06-28.

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Footnotes

1. Although classified as an unbarred spiral${}^{[1]}$ in accordance with optical observations by De Vaucoulers et al. (1991),${}^{[8]}$ more recent near-infrared observations by Beaton et al. (2007) reveal a boxy bulge at the galactic center.${}^{[94]}$ See § Structure for details. ↩

2. Kafle, Prajwal R.; Sharma, Sanjib; Lewis, Geraint F.; et al. (1 February 2018). “The Need for Speed: Escape velocity and dynamical mass measurements of the Andromeda Galaxy”. Monthly Notices of the Royal Astronomical Society. 475 (3): 4043–4054. arXiv:1801.03949. Bibcode:2018MNRAS.475.4043K. doi:10.1093/mnras/sty082. ISSN 0035-8711. S2CID 54039546. ↩ ↩²

3. López-Corredoira, M.; Prieto, C. Allende; Garzón, F.; Wang, H.; Liu, C.; Deng, L. (1 April 2018). “Disk stars in the Milky Way detected beyond 25 kpc from its center”. Astronomy & Astrophysics. 612: L8. arXiv:1804.03064. Bibcode:2018A&A…612L…8L. doi:10.1051/0004-6361/201832880 – via aanda.org. ↩

4. “Milky Way tips the scales at 1.5 trillion solar masses”. Astronomy Now. 11 March 2019. Retrieved 11 September 2024. ↩ ↩²

5. Sawala, Till; Delhomelle, Jehanne; Deason, Alis J.; et al. (2 June 2025). “No certainty of a Milky Way–Andromeda collision”. Nature Astronomy. 9 (8): 1206–1217. arXiv:2408.00064. Bibcode:2025NatAs…9.1206S. doi:10.1038/s41550-025-02563-1. ↩

6. “NASA’s Hubble Shows Milky Way is Destined for Head-On Collision”. NASA. 31 May 2012. Archived from the original on 4 June 2014. Retrieved 12 July 2012. ↩

7. Ueda, Junko; Iono, Daisuke; Yun, Min S.; et al. (2014). “Cold molecular gas in merger remnants. I. Formation of molecular gas disks”. The Astrophysical Journal Supplement Series. 214 (1): 1. arXiv:1407.6873. Bibcode:2014ApJS..214…1U. doi:10.1088/0067-0049/214/1/1. S2CID 716993. ↩

8. Frommert, Hartmut; Kronberg, Christine. “Messier Object Data, sorted by Apparent Visual Magnitude”. SEDS. Retrieved 22 July 2024. ↩

9. “M 31, M 32 & M 110”. Messier Objects Mobile — Charts, Maps & Photos. 15 October 2016. ↩

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