View source for Messier 81

{{Short description|Spiral galaxy in the constellation Ursa Major}}
{{Other uses|M81 (disambiguation)}}
{{Use dmy dates|date=July 2019}}
{{Infobox galaxy
| name = [[Messier object|Messier]] 81
| image = [[File:Messier 81 HST.jpg|300px]]
| caption = The [[Hubble Space Telescope|HST]]'s view of M81, with its open star clusters, globular star clusters, and regions of fluorescent gas.
| epoch = [[Epoch (astronomy)#Julian years and J2000|J2000]]
| constellation name= [[Ursa Major]]<ref name="sinnott1988">
{{cite book
 | first=J. L. E. |last=Dreyer |editor-first=R. W. |editor-last=Sinnott
 | title=The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters 
 | date=1988
 | publisher=[[Sky Publishing Corporation]] / [[Cambridge University Press]]
 | isbn=978-0-933346-51-2
}}</ref>
| ra = {{RA|09|55|33.1730}}<ref name="ned">
{{cite web
 | website = NASA/IPAC Extragalactic Database
 | publisher = [[NASA]] and [[California Institute of Technology|Caltech]]
 | title = Results for Messier 081
 | url = https://ned.ipac.caltech.edu/cgi-bin/objsearch?objname=Messier+081&extend=no&hconst=67.74&omegam=0.3089&omegav=0.6911&corr_z=1&out_csys=Equatorial&out_equinox=J2000.0&obj_sort=RA+or+Longitude&of=pre_text&zv_breaker=30000.0&list_limit=5&img_stamp=YES
 | access-date=2022-11-06
}}</ref>
| dec = {{DEC|+69|03|55.060}}<ref name="ned" />
| size_v = {{Val|26.9|×|14.1|u=arcminute}}<ref name="ned" />
| size = {{convert|29.44|kpc|ly|sigfig=3|abbr=off|lk=on}}<br />(diameter; [[Galaxy#Isophotal diameter|25.0 mag/arcsec<sup>2</sup> B-band isophote]])<ref name="ned" /><ref name=RC3>{{cite book | bibcode=1991rc3..book.....D | year=1991 | title=Third Reference Catalogue of Bright Galaxies | last1=De Vaucouleurs | first1=Gerard | last2=De Vaucouleurs | first2=Antoinette | last3=Corwin | first3=Herold G. | last4=Buta | first4=Ronald J. | last5=Paturel | first5=Georges | last6=Fouque | first6=Pascal }}</ref>
| appmag_v = 6.94<ref name="SIMBAD-M81">{{cite simbad
 |title=M 81
 |access-date=2009-11-28
}}</ref><ref name=GAXEL>
{{cite journal
 |last1=Armando |first1=Gil de Paz |last2=Boissier |first2=Samuel |last3=Madore |first3=Barry F. |last4=Seibert |first4=Mark |last5=Joe |first5=Young H. |last6=Boselli |first6=Alessandro |last7=Wyder |first7=Ted K. |last8=Thilker |first8=David |last9=Bianchi |first9=Luciana |last10=Rey |first10=Soo-Chang |last11=Rich |first11=R. Michael |last12=Barlow |first12=Tom A. |last13=Conrow |first13=Tim |last14=Forster |first14=Karl |last15=Friedman |first15=Peter G. |last16=Martin |first16=D. Christopher |last17=Morrissey |first17=Patrick |last18=Neff |first18=Susan G. |last19=Schiminovich |first19=David |last20=Small |first20=Todd |last21=Donas |first21=José |last22=Heckman |first22=Timothy M. |last23=Lee |first23=Young-Wook |last24=Milliard |first24=Bruno |last25=Szalay |first25=Alex S. |last26=Yi |first26=Sukyoung
 |date=2007
 |title=The GALEX Ultraviolet Atlas of Nearby Galaxies
 |journal=[[Astrophysical Journal]]
 |volume=173
 |issue=2 |pages=185–255
 |arxiv=astro-ph/0606440
 |doi=10.1086/516636
 |bibcode=2007ApJS..173..185G
|s2cid=119085482 }}</ref>
| type = SA(s)ab,<ref name="ned" /> [[LINER]]<ref name="ned" />
| h_radial_v = {{val|-39|3|u=km/s|fmt=commas}}
| z = {{val|0.000130|0.00000900}}<ref name="ned" />
| gal_v = {{val|73|6|u=km/s|fmt=commas}}<ref name="ned" />
| dist_ly = {{convert|3.675 ± 0.049|Mpc|Mly|abbr=on|lk=on|order=flip}}<ref name="ned" />
| names = {{odlist | NGC= 3031 | UGC= 5318 | CGCG= 333-007 | IRAS= 09514+6918 | MCG= +12-10-010 | PGC= 28630 | name= Bode's Galaxy}}{{r|ned|SIMBAD-M81}}
}}

'''Messier 81''' (also known as '''NGC 3031''' or '''Bode's Galaxy''') is a [[grand design spiral galaxy]] about [[1 E22 m|12 million]] [[light-year]]s away in the [[constellation]] [[Ursa Major]]. It has a [[Galaxy#Isophotal diameter|D<sub>25</sub> isophotal diameter]] of {{convert|29.44|kpc|ly|sigfig=3|abbr=off|lk=on}}.<ref name="ned" /><ref name=RC3 /> Because of its relative proximity to the [[Milky Way]] galaxy, large size, and [[active galactic nucleus]] (which harbors a 70 million {{Solar mass|link=y}}<ref name="devereuxetal2003">
{{cite journal
 | first1=N. |last1=Devereux |first2=H. |last2=Ford |first3=Z. |last3=Tsvetanov |first4=J. |last4=Jocoby
 | date=2003
 | title=STIS Spectroscopy of the Central 10 Parsecs of M81: Evidence for a Massive Black Hole
 | journal=[[Astronomical Journal]]
 | volume=125
 | issue=3 | pages=1226–1235
 | bibcode=2003AJ....125.1226D
 | doi=10.1086/367595
| doi-access=|s2cid=121093306 }}</ref>
[[supermassive black hole]]), Messier 81 has been studied extensively by professional [[astronomer]]s. The galaxy's large size and relatively high brightness also makes it a popular target for [[Amateur astronomy|amateur astronomers]].<ref name="omeara1998">

{{cite book
 | first=S. J.
 | last=O'Meara
 | date=1998
 | title=The Messier Objects
 | publisher=[[Cambridge University Press]]
 | isbn=978-0-521-55332-2
 | url-access=registration
 | url=https://archive.org/details/messierobjectsfi00omea
 }}</ref> In late February 2022, astronomers reported that M81 may be the source of [[Fast radio burst#FRB_20200120E|FRB 20200120E]], a repeating [[fast radio burst]].<ref name="SA-20220223" /><ref name="NAT-20220223" />

== Discovery ==
Messier 81 was first discovered by [[Johann Elert Bode]] on 31 December 1774.<ref name="jones1991">
{{cite book
 | first=K. G. |last=Jones
 | date=1991 | edition=2nd
 | title=Messier's Nebulae and Star Clusters
 | publisher=[[Cambridge University Press]]
 | isbn=978-0-521-37079-0
}}</ref>  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 object|Messier Catalogue]].<ref name="jones1991" />

== Visibility ==

The galaxy is to be found approximately 10° northwest of [[Alpha Ursae Majoris]] (Dubhe) along with several other galaxies in the [[Messier 81 Group]].<ref name="omeara1998" /><ref name="eicher1988">
{{cite book
 | first=D. J. |last=Eicher
 | date=1988
 | title=The Universe from Your Backyard
 | url=https://archive.org/details/universefromyour0000eich | url-access=registration | publisher=[[Cambridge University Press]]
 | isbn=978-0-521-36299-3
}}</ref> Its apparent magnitude due to its distance means it requires a [[light pollution|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 [[telescope]]s.<ref name="omeara1998"/><ref name="eicher1988" /> 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.<ref name="omeara1998" /><ref name=uitti>
{{cite web
 |author      = Stephen Uitti
 |url         = http://www.uitti.net/stephen/astro/essays/farthest_naked_eye_object.shtml
 |title       = Farthest Naked Eye Object
 |access-date  = 1 November 2008
|url-status     = live
 |archive-url  = https://web.archive.org/web/20080819153956/http://www.uitti.net/stephen/astro/essays/farthest_naked_eye_object.shtml
 |archive-date = 19 August 2008
}}</ref> Telescopes with [[aperture]]s of {{convert|8|in|cm}} or larger are needed to distinguish structures in the galaxy.<ref name="eicher1988" />

[[Image:Messier81 highres.jpg|thumb|An [[infrared]] image of Messier 81 taken by the [[Spitzer Space Telescope]]. The blue colors represent stellar emission observed at 3.6 [[Micrometre|μm]].<ref name="willneretal2004">
{{cite journal
 | first1=S. P. |last1=Willner |first2=M. L. N. |last2=Ashby |first3=P. |last3=Barmby |first4=G. G. |last4=Fazio |first5=M. |last5=Pahre |first6=H. A. |last6=Smith |first7=R. C. |last7=Kennicutt Jr. |first8=D. |last8=Calzetti |author8-link= Daniela Calzetti |first9=D. A. |last9=Dale |first10=B. T. |last10=Draine |first11=M. W. |last11=Regan |first12=S. |last12=Malhotra |first13=M. D. |last13=Thornley |first14=P. N. |last14=Appleton |first15=D. |last15=Frayer |first16=G. |last16=Helou |first17=S. |last17=Stolovy |first18=L. |last18=Storrie-Lombardi
 | date=2004
 | title=Infrared Array Camera (IRAC) Observations of M81
 | journal=[[Astrophysical Journal Supplement Series]]
 | volume=154
 | issue=1 | pages=222–228
 | bibcode=2004ApJS..154..222W
 | doi=10.1086/422913
 | arxiv=astro-ph/0405626
|s2cid=16609000 }}</ref>  The green colors represent 8 μm emission originating primarily from [[polycyclic aromatic hydrocarbon]]s in the [[interstellar medium]].<ref name="willneretal2004"/>  The red colors represent 24 μm emission originating from heated dust in the interstellar medium.<ref name="gordonetal2004">
{{cite journal
 | first1=K. D. |last1=Gordon |first2=P. G. |last2=Pérez-González |first3=K. A. |last3=Misselt |first4=E. J. |last4=Murphy|first5=G. J. |last5=Bendo |first6=F. |last6=Walter |first7=M. D. |last7=Thornley |first8=R. C. |last8=Kennicutt Jr. |first9=G. H. |last9=Rieke |first10=C. W. |last10=Engelbracht |first11=J.-D. T. |last11=Smith |first12=A. |last12=Alonso-Herrero |author12-link=Almudena Alonso-Herrero|first13=P. N. |last13=Appleton |first14=D. |last14=Calzetti |first15=D. A. |last15=Dale |first16=B. T. |last16=Draine |first17=D. T. |last17=Frayer |first18=G. |last18=Helou |first19=J. L. |last19=Hinz |first20=D. C. |last20=Hines |first21=D. M. |last21=Kelly |first22=J. E. |last22=Morrison |first23=J. |last23=Muzerolle |first24=M. W. |last24=Regan |first25=J. A. |last25=Stansberry |first26=S. R. |last26=Stolovy |first27=L. J. |last27=Storrie-Lombardi |first28=K. Y. L. |last28=Su |first29=E. T. |last29=Young
 | date=2004
 | title=Spatially Resolved Ultraviolet, Hα, Infrared, and Radio Star Formation in M81
 | journal=[[Astrophysical Journal Supplement Series]]
 | volume=154
 | issue=1 | pages=215–221
 | bibcode=2004ApJS..154..215G
 | doi=10.1086/422714
 | arxiv=astro-ph/0406064
|s2cid=17283721 }}</ref>]] The galaxy is best observed during [[April]].<ref>{{cite web | url=https://science.nasa.gov/mission/hubble/science/explore-the-night-sky/hubble-messier-catalog/messier-81/ | title=Messier 81 - NASA Science }}</ref>

== Interstellar dust ==
Most of the emission at infrared wavelengths originates from [[interstellar dust]].<ref name="gordonetal2004"/><ref name="perezgonzalezetal2006">
{{cite journal
 | first1=P. G. |last1=Pérez-González |first2=R. C. |last2=Kennicutt Jr. |first3=K. D. |last3=Gordon |first4=K. A. |last4=Misselt |first5=A. |last5=Gil De Paz |first6=C. W. |last6=Engelbracht |first7=G. H. |last7=Rieke |first8=G. J. |last8=Bendo |first9=L. |last9=Bianchi |first10=S. |last10=Boissier |first11=D. |last11=Calzetti |first12=D. A. |last12=Dale |first13=B. T. |last13=Draine |first14=T. H. |last14=Jarrett |first15=D. |last15=Hollenbach |first16=M. K. M. |last16=Prescott
 | date=2006
 | title=Ultraviolet through Far-Infrared Spatially Resolved Analysis of the Recent Star Formation in M81 (NGC 3031)
 | journal=[[Astrophysical Journal]]
 | volume=648
 | issue=2 | pages=987–1006
 | bibcode=2006ApJ...648..987P
 | doi=10.1086/506196
 | arxiv=astro-ph/0605605
|s2cid=13901458 }}</ref>  This interstellar dust is found primarily within the galaxy's [[spiral arm]]s, and it has been shown to be associated with [[star formation]] regions.<ref name="gordonetal2004"/><ref name="perezgonzalezetal2006"/> The general explanation is that the hot, short-lived [[Stellar classification|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.<ref>{{Cite journal|last1=Chandar|first1=Rupali|last2=Whitmore|first2=Bradley|last3=Lee|first3=Myung Gyoon|date=2004-08-10|title=The Globular Cluster Systems of Five Nearby Spiral Galaxies: New Insights from Hubble Space TelescopeImaging|journal=The Astrophysical Journal|language=en|volume=611|issue=1|pages=220–244|doi=10.1086/421934|arxiv=astro-ph/0407460|bibcode=2004ApJ...611..220C|issn=0004-637X|doi-access=free}}</ref> In late February 2022, astronomers reported that M81 may be the source of [[Fast radio burst#FRB 20200120E|FRB 20200120E]], a repeating [[fast radio burst]].<ref name="SA-20220223">{{cite news |last=Starr |first=Michelle |title=Mysterious Repeating Fast Radio Burst Traced to Very Unexpected Location |url=https://www.sciencealert.com/mysterious-repeating-fast-radio-burst-traced-to-very-unexpected-location |date=23 February 2022 |work=[[ScienceAlert]] |accessdate=24 February 2022 }}</ref><ref name="NAT-20220223">{{cite journal |author=Kirsten, F |display-authors=et al. |title=A repeating fast radio burst source in a globular cluster |url=https://www.nature.com/articles/s41586-021-04354-w |date=23 February 2022 |journal=[[Nature (journal)|Nature]] |volume=602 |issue=7898 |pages=585–589 |doi=10.1038/s41586-021-04354-w |pmid=35197615 |arxiv=2105.11445 |bibcode=2022Natur.602..585K |s2cid=235166402 |accessdate=24 February 2022 }}</ref>

== Supernovae ==
[[File:Bode and Cigar galaxies.jpg|thumb|M81 (left) and [[Messier 82|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.]]
[[Image:M81.jpg|thumb|right|M81 with satellite galaxy [[Holmberg IX]] in the top center-right corner]]
Only one [[supernova]] has been detected in Messier 81.<ref name="nedsn">
{{cite web
 | title=NASA/IPAC Extragalactic Database
 | work=Results for extended name search on NGC 3031
 | url=http://nedwww.ipac.caltech.edu/
 | access-date=2007-02-27
}}</ref>  The supernova, named [[SN 1993J]], was discovered on 28 March 1993 by F.&nbsp;García in [[Spain]].<ref name="iauc5731">
{{cite journal
 | first1=J. |last1=Ripero |first2=F. |last2=Garcia |first3=D. |last3=Rodriguez |first4=P. |last4=Pujol |first5=A. V. |last5=Filippenko |first6=R. R. |last6=Treffers |first7=Y. |last7=Paik |first8=M. |last8=Davis |first9=D. |last9=Schlegel |first10=F. D. A. |last10=Hartwick |first11=D. D. |last11=Balam |first12=D. |last12=Zurek |first13=R. M. |last13=Robb |first14=P. |last14=Garnavich |first15=B. A. |last15=Hong
 | date=1993
 | title=Supernova 1993J in NGC 3031
 | journal=[[IAU Circular]]
 | volume=5731 | pages=1
 | bibcode=1993IAUC.5731....1R
}}</ref> At the time, it was the second brightest Type II supernova observed in the 20th century,<ref name="schmidtetal1993">
{{cite journal
 | last1=Schmidt |first1=B.P. |last2=Kirshner |first2=R.P. |last3=Eastman |first3=R.G. |last4=Grashuis |first4=R. |last5=Dell'Antonio |first5=I. |last6=Caldwell |first6=N. |last7=Foltz |first7=C. |last8=Huchra |first8= John P.|last9=Milone |first9= Alejandra A. E.|date=1993
 | title=The unusual supernova SN1993J in the galaxy M81
 | journal=[[Nature (journal)|Nature]]
 | volume=364
 | issue=6438 | pages=600–602
 | bibcode=1993Natur.364..600S
 | doi=10.1038/364600a0
 |s2cid=4304547 }}</ref> 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.<ref name="schmidtetal1993" /><ref name="filippenkoetal1993">
{{cite journal
 | first1=A. V. |last1=Filippenko |first2=T. |last2=Matheson |first3=L. C. |last3=Ho
 | date=1993
 | title=The "Type IIb" Supernova 1993J in M81: A Close Relative of Type Ib Supernovae
 | journal=[[Astrophysical Journal Letters]]
 | volume=415 | pages=L103–L106
 | bibcode=1993ApJ...415L.103F
 | doi=10.1086/187043
| doi-access=free}}</ref>

Moreover, the variations in SN 1993J's luminosity over time were not like the variations observed in other Type II supernovae,<ref name="bensonetal1994">
{{cite journal
 | first1=P. J. |last1=Benson |first2=W. |last2=Herbst |first3=J. J. |last3=Salzer |first4=G. |last4=Vinton |first5=G. J. |last5=Hanson |first6=S. J. |last6=Ratcliff |first7=P. F. |last7=Winkler |first8=D. M. |last8=Elmegreen |first9=F. |last9=Chromey |first10=C. |last10=Strom |first11=T. J. |last11=Balonek |first12=B. G. |last12=Elmegreen
 | date=1994
 | title=Light curves of SN 1993J from the Keck Northeast Astronomy Consortium
 | journal=[[Astronomical Journal]]
 | volume=107 | pages=1453–1460
 | bibcode=1994AJ....107.1453B
 | doi=10.1086/116958
|doi-access=free }}</ref><ref name="wheeleretal1993">
{{cite journal
 | first1=J. C. |last1=Wheeler |first2=E. |last2=Barker |first3=R. |last3=Benjamin |first4=J. |last4=Boisseau |first5=A. |last5=Clocchiatti |first6=G. |last6=De Vaucouleurs |first7=N. |last7=Gaffney |first8=R. P. |last8=Harkness |first9=A. M. |last9=Khokhlov |first10=D. F. |last10=Lester |first11=B. J. |last11=Smith |first12=V. V. |last12=Smith |first13=J. |last13=Tomkin
 | date=1993
 | title=Early Observations of SN 1993J in M81 at McDonald Observatory
 | journal=[[Astrophysical Journal]]
 | volume=417 | pages=L71–L74
 | bibcode=1993ApJ...417L..71W
 | doi=10.1086/187097
}}</ref> but did resemble the variations observed in Type Ib supernovae.<ref name="richmondetal1994">
{{cite journal
 | first1=M. W. |last1=Richmond |first2=R. R. |last2=Treffers | first3=A. V. |last3=Filippenko |first4=Y. |last4=Palik |first5=B. |last5=Leibundgut |first6=E. |last6=Schulman |first7=C. V. |last7=Cox
 | date=1994
 | title=UBVRI photometry of SN 1993J in M81: The first 120 days
 | journal=[[Astronomical Journal]]
 | volume=107 | pages=1022–1040
 | bibcode=1994AJ....107.1022R
 | doi=10.1086/116915
|doi-access=free }}</ref> Hence, the supernova has been classified as a [[Type IIb supernova|Type IIb]], a transitory class between Type II and Type Ib.<ref name="filippenkoetal1993" /> 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.<ref name="filippenkoetal1993" /><ref name="filippenkoetal1994">
{{cite journal
 | first1=A. V. |last1=Filippenko |first2=T. |last2=Matheson |first3=A. J. |last3=Barth
 | date=1994
 | title=The peculiar type II supernova 1993J in M81: Transition to the nebular phase
 | journal=[[Astronomical Journal]]
 | volume=108 | pages=2220–2225
 | bibcode=1994AJ....108.2220F
 | doi=10.1086/117234
}}</ref> Despite the uncertainties in modeling the unusual supernova, it was also used to estimate a very approximate distance of 8.5 ± 1.3 [[Light-year|Mly]] (2.6 ± 0.4 [[parsec|Mpc]]) to Messier 81.<ref name="schmidtetal1993" /> As a local galaxy, the [[Central Bureau for Astronomical Telegrams]] (CBAT) tracks [[nova]]e in M81 along with [[Andromeda Galaxy|M31]] and [[Triangulum Galaxy|M33]].<ref name="supernovae.net">
{{cite web
 |first       = David
 |last        = Bishop
 |title       = Extragalactic Novae
 |url         = http://www.supernovae.net/novae.html
 |publisher   = supernovae.net (International Supernovae Network)
 |access-date  = 11 September 2010
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20100408150756/http://www.supernovae.net/novae.html
 |archive-date = 8 April 2010
 |df          = dmy-all
}}</ref>

==SMBH==
In the center of M81 there exists a supermassive black hole (SMBH) with a mass of about {{val|7|e=7|u=solar mass}}. The SMBH is active, having an accretion disk and one-sided relativistic [[astrophysical jet|jet]]. The observation also demonstrate that there may exist a second SMBH that orbits the primary SMBH with a period of around 30 years. The mass of the secondary SMBH is estimated at 0.1 of the primary.<ref name="Jiang2023">{{cite journal |last1=Jiang |first1=Wu |last2=Shen |first2=Zhiqiang |last3=Martí-Vidal |first3=Ivan |last4=Yan |first4=Zhen |last5=Huang |first5=Lei |last6=Gold |first6=Roman |last7=Li |first7=Ya-Ping |last8=Xie |first8=Fuguo |last9=Kawaguchi |first9=Noriyuki |title=Observational Evidence of a Centi-parsec Supermassive Black Hole Binary Existing in the Nearby Galaxy M81 |journal=The Astrophysical Journal |date=1 December 2023 |volume=959 |issue=1 |pages=11 |doi=10.3847/1538-4357/ad063d|doi-access=free |arxiv=2312.01328 }}</ref>

== Environment ==
Messier 81 is the largest galaxy in the [[M81 Group]], a [[galaxy group|group]] of 34 in the constellation Ursa Major.<ref name="karachentsev2005">
{{cite journal
 | first=I. D. |last=Karachentsev
 | date=2005
 | title=The Local Group and Other Neighboring Galaxy Groups
 | journal=[[Astronomical Journal]]
 | volume=129
 | issue=1 | pages=178–188
 | bibcode=2005AJ....129..178K
 | doi=10.1086/426368
 | arxiv=astro-ph/0410065
|s2cid=119385141
 }}</ref>  At approximately 11.7 [[light-year|Mly]] (3.6 [[parsec|Mpc]]) from the Earth, it makes this group and the [[Local Group]], containing the [[Milky Way]],<ref name="karachentsev2005" /> relative neighbors in the [[Virgo Supercluster]].

[[interacting galaxy|Gravitational interactions]] of M81 with [[Messier 82|M82]] and [[NGC 3077]]<ref name="yunetal1994">
{{cite journal
 | first1=M. S. |last1=Yun |first2=P. T. P. |last2=Ho |first3=K. Y. |last3=Lo
 | date=1994
 | title=A high-resolution image of atomic hydrogen in the M81 group of galaxies
 | journal=[[Nature (journal)|Nature]]
 | volume=372 | issue=6506 | pages=530–532
 | bibcode=1994Natur.372..530Y
 | doi=10.1038/372530a0
 | pmid=7990925
|s2cid=4369085 }}</ref> have stripped [[hydrogen]] gas away from all three galaxies, forming gaseous filamentary structures in the group.<ref name="yunetal1994" /> Moreover, these interactions have allowed [[interstellar medium|interstellar gas]] to fall into the centers of M82 and NGC 3077, leading to vigorous star formation or [[starburst galaxy|starburst activity]] there.<ref name="yunetal1994" />

== Distance ==
The distance to Messier 81 has been measured by Freedman et al<ref>{{Cite journal |last=Freedman |first=Wendy |date=1994 |title=The Hubble Space Telescope Extragalactic Distance Scale Project. I. The Discovery of Cepheids and a New Distance to M81 |url=https://articles.adsabs.harvard.edu/pdf/1994ApJ...427..628F |journal=The Astrophysical Journal |volume=427 |issue=June |pages=628–655 |doi=10.1086/174172 |bibcode=1994ApJ...427..628F |via=Astrophysics Data System}}</ref> to be 3.63 ± 0.34 [[Megaparsecs]] (11.8 ± 1.1 million [[Light-year|light years]]) by using the [[Hubble Space Telescope]] to identify [[Classical Cepheid variable|classical Cepheid variables]] and measure their periods using the [[period-luminosity relation]] discovered by [[Henrietta Swan Leavitt]].

==See also==
* [[List of galaxies]]
* [[List of Messier objects]]
* [[Messier object]]
* [[New General Catalogue]]

==References==
{{Reflist|30em}}

==External links==
{{Commons}}
* [https://web.archive.org/web/20110722021551/http://blackholes.stardate.org/directory/factsheet.php?p=M81 '''StarDate''': M81 Fact Sheet]
* [http://messier.seds.org/m/m081.html M81, SEDS Messier pages]
* [https://web.archive.org/web/20060619144807/http://www.spitzer.caltech.edu/Media/releases/ssc2003-06/ssc2003-06d.shtml SST: Messier 81]
* {{APOD |date=20 June 2002 |title=Bright Galaxy M81}}
* [http://www.nightskyinfo.com/archive/m81_m82_galaxies NightSkyInfo.com – M81, Bode's Galaxy]{{WikiSky}}
* [https://esahubble.org/images/?search=m81/ ESA/Hubble images of M81]
* [http://ryutao.main.jp/english/st2k_m81_l.html Galaxy Messier 81 (Bode's Galaxy)]
* [https://web.archive.org/web/20070831212827/http://gallery.spitzer.caltech.edu/Imagegallery/image.php?image_name=ssc2003-06d Spitzer Image Gallery]
* [https://web.archive.org/web/20081120150201/http://www.helkit.com/astro/galaxy/m81-82.shtml Helkit Observatory]
* [http://www.starpointing.com/ccd/m81group.html Deep image of the M81 Area]
* [http://www.constellation-guide.com/bodes-galaxy-messier-81/ Bode's Galaxy at Constellation Guide]

{{Messier objects}}
{{List of Seyfert galaxies}}
{{Ursa Major}}
{{Ngc35}}
{{Portal bar|Astronomy|Stars|Outer space}}
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{{Sky|09|55|33.1730|+|69|03|55.060|11800000}}

{{DEFAULTSORT:Messier 081}}
[[Category:Unbarred spiral galaxies]]
[[Category:M81 Group]]
[[Category:Ursa Major]]
[[Category:Messier objects|081]]
[[Category:NGC objects]]
[[Category:UGC objects|05318]]
[[Category:IRAS catalogue objects|09514+6918]]
[[Category:MCG objects|+12-10-010]]
[[Category:Principal Galaxies Catalogue objects|028630]]
[[Category:Discoveries by Johann Elert Bode]]
[[Category:Astronomical objects discovered in 1774|17741231]]