Messier 81

Coordinates: Sky map 09h 55m 33.2s, +69° 03′ 55″
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Messier 81
The HST's view of M81, with its open star clusters, globular star clusters, and regions of fluorescent gas.
Observation data (J2000 epoch)
ConstellationUrsa Major[1]
Right ascension09h 55m 33.2s[2]
Declination+69° 3′ 55″[2]
Heliocentric radial velocity−34
Galactocentric velocity73
Apparent magnitude (V)6.94[3][4]
TypeSA(s)ab,[2] LINER[2]
Size29.44 kiloparsecs (96,000 light-years)
(diameter; 25.0 mag/arcsec2 B-band isophote)[2][5]
Apparent size (V)26.9 × 14.1 moa[2]
Other designations
NGC 3031, UGC 5318, MCG+12-10-010, PGC 28630, Bode's Galaxy[3]

Messier 81 (also known as NGC 3031 or Bode's Galaxy) is a grand design spiral galaxy about 12 million light-years away in the constellation Ursa Major. It has a D25 isophotal diameter of 29.44 kiloparsecs (96,000 light-years).[2][5] Because of its relative proximity to the Milky Way galaxy, large size, and active galactic nucleus (which harbors a 70 million M[6] supermassive black hole), Messier 81 has been studied extensively by professional astronomers. The galaxy's large size and relatively high brightness also makes it a popular target for amateur astronomers.[7] In late February 2022, astronomers reported that M81 may be the source of FRB 20200120E, a repeating fast radio burst.[8][9]


Messier 81 was first discovered by Johann Elert Bode on 31 December 1774.[10] Thus, it is sometimes referred to as "Bode's Galaxy". In 1779, Pierre Méchain and Charles Messier reidentified Bode's object, hence listed it in the Messier Catalogue.[10]


The galaxy is to be found approximately 10° northwest of Alpha Ursae Majoris (Dubhe) along with several other galaxies in the Messier 81 Group.[7][11] Its apparent magnitude due to its distance means it requires a good night sky and only rises very briefly and extremely low at its southernmost limit from Earth's surface, about the 20th parallel south.

Messier 81 and Messier 82 are considered ideal for viewing using binoculars and small telescopes.[7][11] The two objects are generally not observable to the unaided eye, although highly experienced amateur astronomers may be able to see Messier 81 under exceptional observing conditions with a very dark sky.[7][12] Telescopes with apertures of 8 inches (20 cm) or larger are needed to distinguish structures in the galaxy.[11]

An infrared image of Messier 81 taken by the Spitzer Space Telescope. The blue colors represent stellar emission observed at 3.6 μm.[13] The green colors represent 8 μm emission originating primarily from polycyclic aromatic hydrocarbons in the interstellar medium.[13] The red colors represent 24 μm emission originating from heated dust in the interstellar medium.[14]

The galaxy is best observed during April. [15]

Interstellar dust[edit]

Most of the emission at infrared wavelengths originates from interstellar dust.[14][16] This interstellar dust is found primarily within the galaxy's spiral arms, and it has been shown to be associated with star formation regions.[14][16] The general explanation is that the hot, short-lived blue stars that are found within star formation regions are very effective at heating the dust and thus enhancing the infrared dust emission from these regions.

Globular clusters[edit]

It is estimated M81 has 210 ± 30 globular clusters.[17] In late February 2022, astronomers reported that M81 may be the source of FRB 20200120E, a repeating fast radio burst.[8][9]


M81 (left) and M82 (right). M82 is one of two galaxies strongly influenced gravitationally by M81. The other, NGC 3077, is located off the top edge of this image.
M81 with satellite galaxy Holmberg IX in the top center-right corner

Only one supernova has been detected in Messier 81.[18] The supernova, named SN 1993J, was discovered on 28 March 1993 by F. García in Spain.[19] At the time, it was the second brightest supernova observed in the 20th century,[20] peaking at an apparent magnitude of 10.7. The spectral characteristics of the supernova changed over time. Initially, it looked more like a type II supernova (a supernova formed by the explosion of a supergiant star) with strong hydrogen spectral line emission, but later the hydrogen lines faded and strong helium spectral lines appeared, making the supernova look more like a type Ib.[20][21]

Moreover, the variations in SN 1993J's luminosity over time were not like the variations observed in other type II supernovae,[22][23] but did resemble the variations observed in type Ib supernovae.[24] Hence, the supernova has been classified as a type IIb, a transitory class between type II and type Ib.[21] The scientific results from this supernova suggested that type Ib and Ic supernovae were formed through the explosions of giant stars through processes similar to those taking place in type II supernovae.[21][25] Despite the uncertainties in modeling the unusual supernova, it was also used to estimate a very approximate distance of 8.5 ± 1.3 Mly (2.6 ± 0.4 Mpc) to Messier 81.[20] As a local galaxy, the Central Bureau for Astronomical Telegrams (CBAT) tracks novae in M81 along with M31 and M33.[26]


Messier 81 is the largest galaxy in the M81 Group, a group of 34 in the constellation Ursa Major.[27] At approximately 11.7 Mly (3.6 Mpc) from the Earth, it makes this group and the Local Group, containing the Milky Way,[27] relative neighbors in the Virgo Supercluster.

Gravitational interactions of M81 with M82 and NGC 3077[28] have stripped hydrogen gas away from all three galaxies, forming gaseous filamentary structures in the group.[28] Moreover, these interactions have allowed interstellar gas to fall into the centers of M82 and NGC 3077, leading to vigorous star formation or starburst activity there.[28]


The distance to Messier 81 has been measured by Freedman et al[29] to be 3.63 ± 0.34 Megaparsecs (11.8 ± 1.1 million light years) by using the Hubble Space Telescope to identify classical Cepheid variables and measure their periods using the period-luminosity relation discovered by Henrietta Swan Leavitt.

See also[edit]


  1. ^ Dreyer, J. L. E. (1988). Sinnott, R. W. (ed.). The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters. Sky Publishing Corporation / Cambridge University Press. ISBN 978-0-933346-51-2.
  2. ^ a b c d e f g h i j "NASA/IPAC Extragalactic Database". Results for Messier 081. Retrieved 6 November 2022.
  3. ^ a b "M 81". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 28 November 2009.
  4. ^ Armando, Gil de Paz; Boissier, Samuel; Madore, Barry F.; Seibert, Mark; Joe, Young H.; Boselli, Alessandro; Wyder, Ted K.; Thilker, David; Bianchi, Luciana; Rey, Soo-Chang; Rich, R. Michael; Barlow, Tom A.; Conrow, Tim; Forster, Karl; Friedman, Peter G.; Martin, D. Christopher; Morrissey, Patrick; Neff, Susan G.; Schiminovich, David; Small, Todd; Donas, José; Heckman, Timothy M.; Lee, Young-Wook; Milliard, Bruno; Szalay, Alex S.; Yi, Sukyoung (2007). "The GALEX Ultraviolet Atlas of Nearby Galaxies". Astrophysical Journal. 173 (2): 185–255. arXiv:astro-ph/0606440. Bibcode:2007ApJS..173..185G. doi:10.1086/516636. S2CID 119085482.
  5. ^ a b De Vaucouleurs, Gerard; De Vaucouleurs, Antoinette; Corwin, Herold G.; Buta, Ronald J.; Paturel, Georges; Fouque, Pascal (1991). Third Reference Catalogue of Bright Galaxies.
  6. ^ Devereux, N.; Ford, H.; Tsvetanov, Z.; Jocoby, J. (2003). "STIS Spectroscopy of the Central 10 Parsecs of M81: Evidence for a Massive Black Hole". Astronomical Journal. 125 (3): 1226–1235. Bibcode:2003AJ....125.1226D. doi:10.1086/367595. S2CID 121093306.
  7. ^ a b c d O'Meara, S. J. (1998). The Messier Objects. Cambridge University Press. ISBN 978-0-521-55332-2.
  8. ^ a b Starr, Michelle (23 February 2022). "Mysterious Repeating Fast Radio Burst Traced to Very Unexpected Location". ScienceAlert. Retrieved 24 February 2022.
  9. ^ a b Kirsten, F; et al. (23 February 2022). "A repeating fast radio burst source in a globular cluster". Nature. 602 (7898): 585–589. arXiv:2105.11445. Bibcode:2022Natur.602..585K. doi:10.1038/s41586-021-04354-w. PMID 35197615. S2CID 235166402. Retrieved 24 February 2022.
  10. ^ a b Jones, K. G. (1991). Messier's Nebulae and Star Clusters (2nd ed.). Cambridge University Press. ISBN 978-0-521-37079-0.
  11. ^ a b c Eicher, D. J. (1988). The Universe from Your Backyard. Cambridge University Press. ISBN 978-0-521-36299-3.
  12. ^ Stephen Uitti. "Farthest Naked Eye Object". Archived from the original on 19 August 2008. Retrieved 1 November 2008.
  13. ^ a b Willner, S. P.; Ashby, M. L. N.; Barmby, P.; Fazio, G. G.; Pahre, M.; Smith, H. A.; Kennicutt Jr., R. C.; Calzetti, D.; Dale, D. A.; Draine, B. T.; Regan, M. W.; Malhotra, S.; Thornley, M. D.; Appleton, P. N.; Frayer, D.; Helou, G.; Stolovy, S.; Storrie-Lombardi, L. (2004). "Infrared Array Camera (IRAC) Observations of M81". Astrophysical Journal Supplement Series. 154 (1): 222–228. arXiv:astro-ph/0405626. Bibcode:2004ApJS..154..222W. doi:10.1086/422913. S2CID 16609000.
  14. ^ a b c Gordon, K. D.; Pérez-González, P. G.; Misselt, K. A.; Murphy, E. J.; Bendo, G. J.; Walter, F.; Thornley, M. D.; Kennicutt Jr., R. C.; Rieke, G. H.; Engelbracht, C. W.; Smith, J.-D. T.; Alonso-Herrero, A.; Appleton, P. N.; Calzetti, D.; Dale, D. A.; Draine, B. T.; Frayer, D. T.; Helou, G.; Hinz, J. L.; Hines, D. C.; Kelly, D. M.; Morrison, J. E.; Muzerolle, J.; Regan, M. W.; Stansberry, J. A.; Stolovy, S. R.; Storrie-Lombardi, L. J.; Su, K. Y. L.; Young, E. T. (2004). "Spatially Resolved Ultraviolet, Hα, Infrared, and Radio Star Formation in M81". Astrophysical Journal Supplement Series. 154 (1): 215–221. arXiv:astro-ph/0406064. Bibcode:2004ApJS..154..215G. doi:10.1086/422714. S2CID 17283721.
  15. ^
  16. ^ a b Pérez-González, P. G.; Kennicutt Jr., R. C.; Gordon, K. D.; Misselt, K. A.; Gil De Paz, A.; Engelbracht, C. W.; Rieke, G. H.; Bendo, G. J.; Bianchi, L.; Boissier, S.; Calzetti, D.; Dale, D. A.; Draine, B. T.; Jarrett, T. H.; Hollenbach, D.; Prescott, M. K. M. (2006). "Ultraviolet through Far-Infrared Spatially Resolved Analysis of the Recent Star Formation in M81 (NGC 3031)". Astrophysical Journal. 648 (2): 987–1006. arXiv:astro-ph/0605605. Bibcode:2006ApJ...648..987P. doi:10.1086/506196. S2CID 13901458.
  17. ^ Chandar, Rupali; Whitmore, Bradley; Lee, Myung Gyoon (10 August 2004). "The Globular Cluster Systems of Five Nearby Spiral Galaxies: New Insights from Hubble Space TelescopeImaging". The Astrophysical Journal. 611 (1): 220–244. arXiv:astro-ph/0407460. Bibcode:2004ApJ...611..220C. doi:10.1086/421934. ISSN 0004-637X.
  18. ^ "NASA/IPAC Extragalactic Database". Results for extended name search on NGC 3031. Retrieved 27 February 2007.
  19. ^ Ripero, J.; Garcia, F.; Rodriguez, D.; Pujol, P.; Filippenko, A. V.; Treffers, R. R.; Paik, Y.; Davis, M.; Schlegel, D.; Hartwick, F. D. A.; Balam, D. D.; Zurek, D.; Robb, R. M.; Garnavich, P.; Hong, B. A. (1993). "Supernova 1993J in NGC 3031". IAU Circular. 5731: 1. Bibcode:1993IAUC.5731....1R.
  20. ^ a b c Schmidt, B.P.; Kirshner, R.P.; Eastman, R.G.; Grashuis, R.; Dell'Antonio, I.; Caldwell, N.; Foltz, C.; Huchra, John P.; Milone, Alejandra A. E. (1993). "The unusual supernova SN1993J in the galaxy M81". Nature. 364 (6438): 600–602. Bibcode:1993Natur.364..600S. doi:10.1038/364600a0. S2CID 4304547.
  21. ^ a b c Filippenko, A. V.; Matheson, T.; Ho, L. C. (1993). "The "Type IIb" Supernova 1993J in M81: A Close Relative of Type Ib Supernovae". Astrophysical Journal Letters. 415: L103–L106. Bibcode:1993ApJ...415L.103F. doi:10.1086/187043.
  22. ^ Benson, P. J.; Herbst, W.; Salzer, J. J.; Vinton, G.; Hanson, G. J.; Ratcliff, S. J.; Winkler, P. F.; Elmegreen, D. M.; Chromey, F.; Strom, C.; Balonek, T. J.; Elmegreen, B. G. (1994). "Light curves of SN 1993J from the Keck Northeast Astronomy Consortium". Astronomical Journal. 107: 1453–1460. Bibcode:1994AJ....107.1453B. doi:10.1086/116958.
  23. ^ Wheeler, J. C.; Barker, E.; Benjamin, R.; Boisseau, J.; Clocchiatti, A.; De Vaucouleurs, G.; Gaffney, N.; Harkness, R. P.; Khokhlov, A. M.; Lester, D. F.; Smith, B. J.; Smith, V. V.; Tomkin, J. (1993). "Early Observations of SN 1993J in M81 at McDonald Observatory". Astrophysical Journal. 417: L71–L74. Bibcode:1993ApJ...417L..71W. doi:10.1086/187097.
  24. ^ Richmond, M. W.; Treffers, R. R.; Filippenko, A. V.; Palik, Y.; Leibundgut, B.; Schulman, E.; Cox, C. V. (1994). "UBVRI photometry of SN 1993J in M81: The first 120 days". Astronomical Journal. 107: 1022–1040. Bibcode:1994AJ....107.1022R. doi:10.1086/116915.
  25. ^ Filippenko, A. V.; Matheson, T.; Barth, A. J. (1994). "The peculiar type II supernova 1993J in M81: Transition to the nebular phase". Astronomical Journal. 108: 2220–2225. Bibcode:1994AJ....108.2220F. doi:10.1086/117234.
  26. ^ Bishop, David. "Extragalactic Novae". (International Supernovae Network). Archived from the original on 8 April 2010. Retrieved 11 September 2010.
  27. ^ a b Karachentsev, I. D. (2005). "The Local Group and Other Neighboring Galaxy Groups". Astronomical Journal. 129 (1): 178–188. arXiv:astro-ph/0410065. Bibcode:2005AJ....129..178K. doi:10.1086/426368. S2CID 119385141.
  28. ^ a b c Yun, M. S.; Ho, P. T. P.; Lo, K. Y. (1994). "A high-resolution image of atomic hydrogen in the M81 group of galaxies". Nature. 372 (6506): 530–532. Bibcode:1994Natur.372..530Y. doi:10.1038/372530a0. PMID 7990925. S2CID 4369085.
  29. ^ Freedman, Wendy (1994). "The Hubble Space Telescope Extragalactic Distance Scale Project. I. The Discovery of Cepheids and a New Distance to M81". The Astrophysical Journal. 427 (June): 628–655. Bibcode:1994ApJ...427..628F. doi:10.1086/174172 – via Astrophysics Data System.

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