MESSIER 81

'Messier 81' (also known as '''NGC 3031''' or '''Bode's Galaxy''') is a spiral galaxy about 12 million light-years away in the constellation Ursa Major. M81 is one of the most striking examples of a grand design spiral galaxy, with near perfect arms spiraling into the very center. Because of its close proximity to Earth, its large size, and its active galactic nucleus (which may harbor a supermassive black hole) Messier 81 is a popular galaxy to study in professional astronomy research. The galaxy's large size and relatively high apparent magnitude also make it a popular target for amateur astronomy observations.^[1]

Contents

Discovery

Dust emission

Supernova

Nearby galaxies and galaxy group information

Amateur astronomy information

See also

External links

References

Discovery

Messier 81 was first discovered by Johann Elert Bode in 1774^[2]. Consequently, the galaxy is sometimes referred to as "Bode's Galaxy". In 1779, Pierre Méchain and Charles Messier reidentified Bode's object, which was subsequently listed in the Messier Catalogue².

Dust emission

Most of the emission at infrared wavelengths originates from interstellar dust.^[5] This interstellar dust is found primarily within the galaxy's spiral arms, and it has been shown to be associated with star formation regions. 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 hence enhancing the infrared dust emission from these regions.

Supernova

Only one supernova has been detected in Messier 81^[6]. The supernova, named SN 1993J, was discovered on 28 March 1993 by F. Garcia in Spain^[7]. At the time, it was the second brightest supernova observed in the twentieth century^[8]. The spectral characteristics of the supernova changed over time. Initially, it looked more like a type II supernova (a supernovae formed by the explosion of a giant 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^8[9]. Moreover, the variations in SN 1993J's luminosity over time were not like the variations observed in other type II supernovae^[10][11] but did resemble the variations observed in type Ib supernovae^[12]. Hence, the supernova has been classified as a "type IIb", a transitory class between type II and type Ib⁹. The scientific results from this supernova suggested that type Ib and Ic supernovae were actually formed through the explosions of giant stars through processes similar to what takes place in type II supernovae^9[13]. The supernova was also used to estimate a distance of 8.5 ± 1.3 Mly (2.6 ± 0.4 Mpc) to Messier 81⁸.

Nearby galaxies and galaxy group information

Messier 81 is the largest galaxy in the M81 Group, a group of 34 galaxies located in the constellation Ursa Major^[14]. The distance from the Earth to the group is approximately 11.7 Mly (3.6 Mpc), making this one of the closest groups to the Local Group, which contains the Milky Way¹⁴.
M81 is gravitationally interacting with Messier 82 and NGC 3077^[15]. The interactions have stripped some hydrogen gas away from all three galaxies, leading to the formation of filamentary gas structures in the group¹⁵. Moreover, the interactions have also caused some interstellar gas to fall into the centers of Messier 82 and NGC 3077, which has led to strong starburst activity (or the formation of many stars) within the centers of these two galaxies¹⁵.

Amateur astronomy information

Messier 81, Messier 82, and several other galaxies in the Messier 81 Group are located approximately 10° northwest of Alpha Ursae Majoris.^[16] Messier 81 and Messier 82 can both be viewed easily using binoculars and small telescopes. The two objects are generally not observable unaided by the average amateur astronomer, although highly experienced amateur astronomers may be able to see Messier 81 under exceptional observing conditions. Although the galaxy is visible in small telescopes, telescopes with apertures of 8 in or larger are needed to distinguish structure in Messier 81.

See also

★ M81 in fiction ''(in the galaxies in fiction article)''

External links

★ M81, SEDS Messier pages

★ 'SST': Messier 81

★ 'APOD': Bright Galaxy M81 (6/20/02)

★ NightSkyInfo.com - M81, Bode's Galaxy

★ 'WIKISKY.ORG': SDSS image M81

★ ESA/Hubble images of M81

★ Galaxy Messier 81 (Bode's Galaxy) at the astro-photography site of 'Mr. Takayuki Yoshida.'

★ Spitzer Image Gallery

References

1. The Messier Objects, S. J. O'Meara, , , Cambridge University, 1998, ISBN 0-521-55332-6
2. Messier's Nebulae and Star Clusters, K. G. Jones, , , Cambridge University Press, 1991, ISBN 0-521-37079-5
3. Infrared Array Camera (IRAC) Observations of M81, S. P. Willner, M. L. N. Ashby, P. Barmby, G. G. Fazio, M. Pahre, H. A. Smith, R. C. Kennicutt, Jr., D. Calzetti, D. A. Dale, B. T. Draine, M. W. Regan, S. Malhotra, M. D. Thornley, P. N. Appleton, D. Frayer, G. Helou, S. Stolovy, and L. Storrie-Lombardi, , , Astrophysical Journal Supplement Series, 2004
4. Spatially Resolved Ultraviolet, Hα, Infrared, and Radio Star Formation in M81, K. D. Gordon, P. G. Pérez-González, K. A. Misselt, E. J. Murphy, G. J. Bendo, F. Walter, M. D. Thornley, R. C. Kennicutt, Jr., G. H. Rieke, C. W. Engelbracht, J.-D. T. Smith, A. Alonso-Herrero, P. N. Appleton, D. Calzetti, D. A. Dale, B. T. Draine, D. T. Frayer, G. Helou, J. L. Hinz, D. C. Hines, D. M. Kelly, J. E. Morrison, J. Muzerolle, M. W. Regfan, J. A. Stansberry, S. R. Stolovy, L. J. Storrie-Lombardi, K. Y. L. Su, E. T. Young, , , Astrophysical Journal Supplement Series, 2004
5. Ultraviolet through Far-Infrared Spatially Resolved Analysis of the Recent Star Formation in M81 (NGC 3031), P. G. Pérez-González, R. C. Kennicutt, Jr., K. D. Gordon, K. A. Misselt, A. Gil de Paz, C. W. Engelbracht, G. H. Rieke, G. J. Bendo, L. Bianchi, S. Bossier, D. Calzetti, D. A. Dale, B. T. Draine, T. H. Jarrett, D. Hollenbach, M. K. M. Prescott, , , Astrophysical Journal, 2006
6. NASA/IPAC Extragalactic Database
7. Supernova 1993J in NGC 3031, J. Ripero, F. Garcia, D. Rodriguez, P. Pujol, A. V. Filippenko, R. R. Treffers, Y. Paik, M. Davis, D. Schlegel, F. D. A. Hartwick, D. D. Balam, D. Zurek, R. M. Robb, P. Garnavich, B. A. Hong, , , IAU Circular, 1993
8. The unusual supernova SN1993J in the galaxy M81, B. P. Schmidt, R. P. Kirshner, R. G. Eastman, R. Grashuis, I. dell'Antonio, N. Caldwell, C. Foltz, J. P. Huchra, A. A. E. Milone, , , Nature, 1993
9. The "Type IIb" Supernova 1993J in M81: A Close Relative of Type Ib Supernovae, A. V. Filippenko, T. Matheson, L. C. Ho, , , Astrophysical Journal Letters, 1993
10. Light curves of SN 1993J from the Keck Northeast Astronomy Consortium, P. J. Benson, W. Herbst, J. J> Salzer, G. Vinton, G. J. Hanson, S. J. Ratcliff, P. F. Winkler, D. M. Elmegreen, F. Chromey, C. Strom, T. J. Balonek, B. G. Elmegreen, , , Astronomical Journal, 1994
11. Early Observations of SN 1993J in M81 at McDonald Observatory, J. C. Wheeler, E. Barker, R. Benjamin, J. Boisseau, A. Clocchiatti, G. de Vaucouleurs, N. Gaffney, R. P. Harkness, A. M. Khokhlov, D. F. Lester, B. J> Smith, V. V. Smith, J. Tomkin, , , Astrophysical Journal, 1993
12. UBVRI photometry of SN 1993J in M81: The first 120 days, M. W. Richmond, R. R. Treffers, A. V. Filippenko, Y. Palik, B. Leibundgut, E. Schulman, C. V. Cox, , , Astronomical Journal, 1994
13. The peculiar type II supernova 1993J in M81: Transition to the nebular phase, A. V. Filippenko, T. Matheson, A. J. Barth, , , Astronomical Journal, 1994
14. The Local Group and Other Neighboring Galaxy Groups, I. D. Karachentsev, , , Astronomical Journal, 2005
15. A high-resolution image of atomic hydrogen in the M81 group of galaxies, M. S. Yun, P. T. P. Ho, K. Y. Lo, , , Nature, 1994
16. The Universe from Your Backyard, D. J. Eicher, , , Cambridge University Press, 1988, ISBN 0-521-36299-7