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]
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
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]
Supernovae
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
hydrogenspectral 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]
Environment
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.
^
abc
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.
S2CID17283721.
^
ab
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.
S2CID13901458.
^
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.
^
abc
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.
S2CID4304547.
^
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.
^
Bishop, David.
"Extragalactic Novae". supernovae.net (International Supernovae Network). Archived from
the original on 8 April 2010. Retrieved 11 September 2010.