Messier 81

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Spiral galaxy in the constellation Ursa Major

title: "Messier 81" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["unbarred-spiral-galaxies", "m81-group", "ursa-major", "messier-objects", "ngc-objects", "ugc-objects", "iras-catalogue-objects", "mcg-objects", "principal-galaxies-catalogue-objects", "discoveries-by-johann-elert-bode", "astronomical-objects-discovered-in-1774"] description: "Spiral galaxy in the constellation Ursa Major" topic_path: "science/astronomy" source: "https://en.wikipedia.org/wiki/Messier_81" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Spiral galaxy in the constellation Ursa Major ::

::data[format=table title="Infobox galaxy"]

Field	Value
name	Messier 81
image	[[File:Messier 81 HST.jpg
caption	The HST's view of M81, with its open star clusters, globular star clusters, and regions of fluorescent gas.
epoch	J2000
constellation name	Ursa Major
first	J. L. E.
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
ra
website	NASA/IPAC Extragalactic Database
publisher	NASA and 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
dec
size_v
size	29.44 kpc
(diameter; 25.0 mag/arcsec2 B-band isophote)
appmag_v	6.94{{cite simbad
title	M 81
access-date	2009-11-28
}}<ref name	GAXEL
last1	Armando
date	2007
title	The GALEX Ultraviolet Atlas of Nearby Galaxies
journal	Astrophysical Journal
volume	173
issue	2
arxiv	astro-ph/0606440
doi	10.1086/516636
bibcode	2007ApJS..173..185G
s2cid	119085482 }}
type	SA(s)ab, LINER
h_radial_v
z
gal_v
dist_ly	3.675 ± 0.049 Mpc
names
::

| name = Messier 81 | image = [[File:Messier 81 HST.jpg|300px]] | caption = The HST's view of M81, with its open star clusters, globular star clusters, and regions of fluorescent gas. | epoch = J2000 | constellation name= Ursa Major | 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 | ra = | website = NASA/IPAC Extragalactic Database | publisher = NASA and 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 | dec = | size_v = | size = 29.44 kpc (diameter; 25.0 mag/arcsec2 B-band isophote) | appmag_v = 6.94{{cite simbad |title=M 81 |access-date=2009-11-28 |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 }} | type = SA(s)ab, LINER | h_radial_v = | z = | gal_v = | dist_ly = 3.675 ± 0.049 Mpc | names =

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 kpc. Because of its relative proximity to the Milky Way galaxy, large size, and active galactic nucleus (which harbors a 70 million | 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 }} 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.

Discovery

Visibility

Messier 81 and Messier 82 are considered ideal for viewing using binoculars and small telescopes. 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. |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

::figure[src="https://upload.wikimedia.org/wikipedia/commons/4/4d/Messier81_highres.jpg" caption="μm]]."] ::

| 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 }} The green colors represent 8 μm emission originating primarily from polycyclic aromatic hydrocarbons in the interstellar medium. The red colors represent 24 μm emission originating from heated dust in the interstellar medium. | 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 }}]] The galaxy is best observed during April.

Interstellar dust

Most of the emission at infrared wavelengths originates from interstellar dust. | 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 }} 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 thus enhancing the infrared dust emission from these regions.

Globular clusters

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

Supernovae

::figure[src="https://upload.wikimedia.org/wikipedia/commons/e/e1/Bode_and_Cigar_galaxies.jpg" caption="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."] ::

::figure[src="https://upload.wikimedia.org/wikipedia/commons/8/8b/M81.jpg" caption="M81 with satellite galaxy [[Holmberg IX]] in the top center-right corner"] ::

Only one supernova has been detected in Messier 81. | 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 | 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 | 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 | volume=364 | issue=6438 | pages=600–602 | bibcode=1993Natur.364..600S | doi=10.1038/364600a0 |s2cid=4304547 }} 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. | 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}}

Moreover, the variations in SN 1993J's luminosity over time were not like the variations observed in other Type II supernovae, | 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 }} | 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 | 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 }} Hence, the supernova has been classified as a Type IIb, a transitory class between Type II and Type Ib. 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. | 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 |first = David |last = Bishop |title = Extragalactic Novae |url = https://www.rochesterastronomy.org/novae.html |publisher = Rochester Astronomy |access-date = 27 January 2026 |df = dmy-all

SMBH

In the center of M81 there exists a supermassive black hole (SMBH) with a mass of about . The SMBH is active, having an accretion disk and one-sided relativistic 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.

Environment

Gravitational interactions of M81 with M82 and NGC 3077 | 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 | volume=372 | issue=6506 | pages=530–532 | bibcode=1994Natur.372..530Y | doi=10.1038/372530a0 | pmid=7990925 |s2cid=4369085 }} have stripped hydrogen gas away from all three galaxies, forming gaseous filamentary structures in the group. 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.

Distance

The distance to Messier 81 has been measured by Freedman et al 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.

References

(1991). "Third Reference Catalogue of Bright Galaxies".
"Messier 81 - NASA Science".
(2004-08-10). "The Globular Cluster Systems of Five Nearby Spiral Galaxies: New Insights from Hubble Space TelescopeImaging". The Astrophysical Journal.
Starr, Michelle. (23 February 2022). "Mysterious Repeating Fast Radio Burst Traced to Very Unexpected Location". [[ScienceAlert]].
Kirsten, F. (23 February 2022). "A repeating fast radio burst source in a globular cluster". [[Nature (journal).
(1 December 2023). "Observational Evidence of a Centi-parsec Supermassive Black Hole Binary Existing in the Nearby Galaxy M81". The Astrophysical Journal.
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.

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