Messier 81
Encyclopedia
Messier 81 is a spiral galaxy
about 12 million
light-year
s away in the constellation
Ursa Major
. Due to its proximity to Earth
, large size and active galactic nucleus
(which harbors a 70 million M☉
supermassive black hole
), Messier 81 has been studied extensively by professional astronomers. The galaxy's large size and relatively high brightness also make it a popular target for amateur astronomers
.
in 1774. 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 Catalogue.
Most of the emission at infrared
wavelengths originates from interstellar dust. 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 star
s that are found within star formation regions are very effective at heating the dust and hence enhancing the infrared dust emission from these regions.
has been detected in Messier 81. The supernova, named SN 1993J
, was discovered on 28 March 1993 by F. Garcia in Spain. At the time, it was the second brightest supernova observed in the twentieth century. 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. Moreover, the variations in SN 1993J's luminosity over time were not like the variations observed in other type II supernovae but did resemble the variations observed in type Ib supernovae. 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 actually formed through the explosions of giant stars through processes similar to what takes place in type II supernovae. The supernova was also used to estimate a distance of 8.5 ± 1.3 Mly (2.6 ± 0.4 Mpc
) to Messier 81. As a local galaxy, the Central Bureau for Astronomical Telegrams
(CBAT) tracks nova
e in M81 along with M31
and M33
.
Messier 81 is the largest galaxy in the M81 Group
, a group
of 34 galaxies located in the constellation Ursa Major. 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 Way
.
M81 is gravitationally interacting
with Messier 82
and NGC 3077
. The interactions have stripped some hydrogen
gas away from all three galaxies, leading to the formation of filamentary gas structures in the group. 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 galaxies.
and small telescope
s. 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. Telescopes with aperture
s of 8 inches or larger are needed to distinguish structures in the galaxy.
Spiral galaxy
A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as...
about 12 million
1 E22 m
To help compare different orders of magnitude, this page lists distances starting at 10 Zm .Distances shorter than 10 Zm* 24 Zm — 2.5 million light years — Distance to the Andromeda Galaxy...
light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s away in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Ursa Major
Ursa Major
Ursa Major , also known as the Great Bear, is a constellation visible throughout the year in most of the northern hemisphere. It can best be seen in April...
. Due to its proximity to Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
, large size and active galactic nucleus
Active galactic nucleus
An active galactic nucleus is a compact region at the centre of a galaxy that has a much higher than normal luminosity over at least some portion, and possibly all, of the electromagnetic spectrum. Such excess emission has been observed in the radio, infrared, optical, ultra-violet, X-ray and...
(which harbors a 70 million M☉
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
supermassive black hole
Supermassive black hole
A supermassive black hole is the largest type of black hole in a galaxy, in the order of hundreds of thousands to billions of solar masses. Most, and possibly all galaxies, including the Milky Way, are believed to contain supermassive black holes at their centers.Supermassive black holes have...
), Messier 81 has been studied extensively by professional astronomers. The galaxy's large size and relatively high brightness also make it a popular target for amateur astronomers
Amateur astronomy
Amateur astronomy, also called backyard astronomy and stargazing, is a hobby whose participants enjoy watching the night sky , and the plethora of objects found in it, mainly with portable telescopes and binoculars...
.
Discovery
Messier 81 was first discovered by Johann Elert BodeJohann Elert Bode
Johann Elert Bode was a German astronomer known for his reformulation and popularization of the Titius-Bode law. Bode determined the orbit of Uranus and suggested the planet's name.-Biography:...
in 1774. Consequently, the galaxy is sometimes referred to as "Bode's Galaxy". In 1779, Pierre Méchain
Pierre Méchain
Pierre François André Méchain was a French astronomer and surveyor who, with Charles Messier, was a major contributor to the early study of deep sky objects and comets.-Life:...
and Charles Messier
Charles Messier
Charles Messier was a French astronomer most notable for publishing an astronomical catalogue consisting of deep sky objects such as nebulae and star clusters that came to be known as the 110 "Messier objects"...
reidentified Bode's object, which was subsequently listed in the Messier Catalogue.
Dust emission
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
wavelengths originates from interstellar dust. This interstellar dust is found primarily within the galaxy's spiral arms, and it has been shown to be associated with star formation
Star formation
Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. As a branch of astronomy star formation includes the study of the interstellar medium and giant molecular clouds as precursors to the star formation process and the study of young...
regions. The general explanation is that the hot, short-lived blue star
Blue star
A blue star is a type of star.Blue star or bluestar may also refer to:The Blue Star Is Kind Of Shiny It Is All Of Stars To Protect The Moon-Music:* Bluestar Entertainment, record label* "Blue Star" , first recorded 1955...
s 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 supernovaSupernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
has been detected in Messier 81. The supernova, named SN 1993J
SN 1993J
SN 1993J is a supernova observed in the galaxy M81. It was discovered on 28 March 1993 by F. Garcia in Spain. At the time, it was the second brightest supernova observed in the twentieth century behind SN 1987A....
, was discovered on 28 March 1993 by F. Garcia in Spain. At the time, it was the second brightest supernova observed in the twentieth century. 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
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
spectral line
Spectral line
A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from a deficiency or excess of photons in a narrow frequency range, compared with the nearby frequencies.- Types of line spectra :...
emission, but later the hydrogen lines faded and strong helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
spectral lines appeared, making the supernova look more like a type Ib. Moreover, the variations in SN 1993J's luminosity over time were not like the variations observed in other type II supernovae but did resemble the variations observed in type Ib supernovae. 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 actually formed through the explosions of giant stars through processes similar to what takes place in type II supernovae. The supernova was also used to estimate a distance of 8.5 ± 1.3 Mly (2.6 ± 0.4 Mpc
Parsec
The parsec is a unit of length used in astronomy. It is about 3.26 light-years, or just under 31 trillion kilometres ....
) to Messier 81. As a local galaxy, the Central Bureau for Astronomical Telegrams
Central Bureau for Astronomical Telegrams
The Central Bureau for Astronomical Telegrams is the official international clearing house for information relating to transient astronomical events....
(CBAT) tracks nova
Nova
A nova is a cataclysmic nuclear explosion in a star caused by the accretion of hydrogen on to the surface of a white dwarf star, which ignites and starts nuclear fusion in a runaway manner...
e in M81 along with M31
Andromeda Galaxy
The Andromeda Galaxy is a spiral galaxy approximately 2.5 million light-years from Earth in the constellation Andromeda. It is also known as Messier 31, M31, or NGC 224, and is often referred to as the Great Andromeda Nebula in older texts. Andromeda is the nearest spiral galaxy to the...
and M33
Triangulum Galaxy
The Triangulum Galaxy is a spiral galaxy approximately 3 million light years from Earth in the constellation Triangulum. It is catalogued as Messier 33 or NGC 598, and is sometimes informally referred to as the Pinwheel Galaxy, a nickname it shares with Messier 101...
.
M81 Group
M81 Group
The M81 Group is a group of galaxies in the constellation Ursa Major that includes the well-known galaxies Messier 81 and Messier 82, as well as several other galaxies with high apparent brightnesses. The approximate center of the group is located at a distance of 3.6 Mpc, making it one of the...
, a group
Galaxy groups and clusters
Galaxy groups and clusters are the largest known gravitationally bound objects to have arisen thus far in the process of cosmic structure formation. They form the densest part of the large scale structure of the universe...
of 34 galaxies located in the constellation Ursa Major. The distance from the Earth to the group is approximately 11.7 Mly
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
(3.6 Mpc
Parsec
The parsec is a unit of length used in astronomy. It is about 3.26 light-years, or just under 31 trillion kilometres ....
), making this one of the closest groups to the Local Group
Local Group
The Local Group is the group of galaxies that includes Earth's galaxy, the Milky Way. The group comprises more than 30 galaxies , with its gravitational center located somewhere between the Milky Way and the Andromeda Galaxy...
, which contains the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
.
M81 is gravitationally interacting
Interacting galaxy
Interacting galaxies are galaxies whose gravitational fields result in a disturbance of one another. An example of a minor interaction is a satellite galaxy's disturbing the primary galaxy's spiral arms. An example of a major interaction is a galactic collision.-Satellite interaction:A giant...
with Messier 82
Messier 82
Messier 82 is the prototype nearby starburst galaxy about 12 million light-years away in the constellation Ursa Major...
and NGC 3077
NGC 3077
NGC 3077 is a smaller member of the M81 Group. It looks much like an elliptical galaxy. However, it is peculiar for two reasons. First, it shows wispy edges and scattered dust clouds that are probably a result of gravitational interaction with its larger neighbors, similar to the galaxy M82....
. The interactions have stripped some hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
gas away from all three galaxies, leading to the formation of filamentary gas structures in the group. Moreover, the interactions have also caused some interstellar gas
Interstellar medium
In astronomy, the interstellar medium is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space...
to fall into the centers of Messier 82 and NGC 3077, which has led to strong starburst activity
Starburst galaxy
A starburst galaxy is a galaxy in the process of an exceptionally high rate of star formation, compared to the usual star formation rate seen in most galaxies. Galaxies are often observed to have a burst of star formation after a collision or close encounter between two galaxies...
(or the formation of many stars) within the centers of these two galaxies.
Amateur astronomy
Messier 81 is located approximately 10° northwest of Alpha Ursae Majoris along with several other galaxies in the Messier 81 Group. Messier 81 and Messier 82 can both be viewed easily using binocularsBinoculars
Binoculars, field glasses or binocular telescopes are a pair of identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, allowing the viewer to use both eyes when viewing distant objects...
and small telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
s. 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. Telescopes with aperture
Aperture
In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are,...
s of 8 inches or larger are needed to distinguish structures in the galaxy.
See also
- M81 in fiction (in the galaxies in fictionGalaxies in fictionGalaxies other than the Milky Way are popular settings for creators of science fiction, particularly those working with broad-scale space opera settings. Among the most common settings are the Andromeda Galaxy, the Magellanic Clouds, and the Triangulum Galaxy, all part of the Local Group close to...
article) - Bode's GalaxyGalaxies named after peopleA small number of galaxies or galaxy groups have been named after individual people. In most cases, the named individual was the person who discovered the object, who first brought attention to it, or who first studied it scientifically....
- Messier objectMessier objectThe Messier objects are a set of astronomical objects first listed by French astronomer Charles Messier in 1771. The original motivation of the catalogue was that Messier was a comet hunter, and was frustrated by objects which resembled but were not comets...
- List of Messier objects
- New General CatalogueNew General CatalogueThe New General Catalogue of Nebulae and Clusters of Stars is a well-known catalogue of deep sky objects in astronomy. It contains 7,840 objects, known as the NGC objects...
- List of galaxies