Whirlpool Galaxy
Encyclopedia
The Whirlpool Galaxy is an interacting
grand-design
spiral galaxy
that is estimated to be 23 ± 4 million light-year
s from the Milky Way Galaxy. in the constellation
Canes Venatici
. It is one of the most famous galaxies in the sky.
The galaxy and its companion (NGC 5195
) are easily observed by amateur astronomers
, and the two galaxies may even be seen with binoculars
. The Whirlpool Galaxy is also a popular target for professional astronomers, who study it to further understand galaxy structure (particularly structure associated with the spiral arms) and galaxy interactions.
What was later known as the Whirlpool Galaxy was discovered on October 13, 1773 by Charles Messier
, and is designated as M51
. Its companion galaxy, NGC 5195
, was discovered in 1781 by Pierre Méchain
. It was however not until 1845 that the Whirlpool became the first to be recognized as a spiral. This was achieved by Lord Rosse
employing a 72-inch (~1.83 m) reflecting telescope which he constructed at Birr Castle
, Ireland. Sometimes M51 is used to refer to the pair of galaxies, in which case the individual galaxies may be referred to as M51A (NGC 5194) and M51B (NGC 5195).
In 2005 a supernova
(SN 2005cs
) was observed in the Whirlpool Galaxy, peaking at apparent magnitude
14.
On 31 May 2011 a magnitude 13.5 type II supernova
(SN 2011dh
) was detected in M51 at coordinates 13:30:05.08 +47:10:11.2.
is estimated to be 160 billion solar masses.
A black hole
, surrounded by a ring of dust, is thought to exist at the heart of the spiral. The dust ring stands almost perpendicular to the relatively flat spiral nebula. A secondary ring crosses the primary ring on a different axis, a phenomenon that is contrary to expectations. A pair of ionization cone
s extend from the axis of the main dust ring.
, M51 is found by following the easternmost star of the Big Dipper
, Eta Ursae Majoris
, and going 3.5° southeast. Its declination is +47°, making it a circumpolar
for observers located above 43°N latitude; it reaches high altitudes throughout the northern hemisphere making it an accessible object from the early hours in winter through the end of spring season, after which observation is hindered in lower latitudes.
M51 is visible through binoculars under dark sky conditions
and can be resolved in detail with modern amateur telescopes. When seen through a 100 mm telescope the basic outlines of M51 and its companion are visible. Under dark skies, and with a moderate eyepiece through a 150 mm telescope, M51's intrinsic spiral structure can be detected. With larger (>300 mm) instruments under dark sky conditions, the various spiral bands are apparent with HII regions visible, and M51 can be seen to be attached to M51B.
As is usual for galaxies, the true extent of its structure can only be gathered from inspecting photographs; long exposures reveal a large nebula extending beyond the visible circular appearance.
In January 2005 the Hubble Heritage Project
constructed a 11477x7965 pixel composite image (shown in the info box above) of M51 using Hubble's ACS instrument
.
.
Generally speaking, hydrogen gas is the most common component of the interstellar medium
(the vast space between stars and planetary systems in galaxies). It exists primarily in its atomic and molecular form, and forms huge clouds throughout the entire galaxy. When large sources of gravitational pull pass nearby, such as other galaxies, gravitational interactions produce compression (density) waves that sweep through these hydrogen clouds. This causes some regions of the previously diffuse gas to compress into tight pockets of opaque and dense gas, these are dust lanes one so often sees in the spiral arms. In regions where the concentration and density of gas reaches a critical value, further collapse under its own gravitational pull occurs, and stars are born at the center of the collapse, where the gas is compressed so strongly that fusion
initiates.
When this happens, these new-born stars consume huge amounts of gas causing them to expand, shine even hotter, and finally sweep away the surrounding layers of dust and gas by increasing efflux of the stellar wind. The gigantic proportions of the clouds out of which they are born means stars seldom, if ever, are created in isolation. Thus regions of several hot young stars emit sufficient light energy that they can be seen in the high resolution pictures of M51 across millions of lightyears distance.
For an example of such a formation in our own galaxy, see M16, the Eagle Nebula
.
Recent simulations bear out that M51's spiral structure was caused by NGC 5195 passing through the main disk of M51 about 500 to 600 million years ago. In this model, NGC 5195 came from behind M51 through the disk towards the observer and made another disk crossing as recently as 50 to 100 million years ago until it is where we observe it to be now, slightly behind M51.
, a small group of galaxies that also includes M63 (the Sunflower Galaxy), NGC 5023
, and NGC 5229
. This small group may actually be a subclump at the southeast end of a large, elongated group that includes the M101 Group
and the NGC 5866 Group
, although most group identification methods and catalogs identify the three groups as separate entities.
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...
grand-design
Grand design spiral galaxy
A grand design spiral galaxy is a type of spiral galaxy with prominent and well-defined spiral arms, as opposed to multi-arm and flocculent spirals which have subtler structural features. The spiral arms of a grand design galaxy extend clearly around the galaxy through many radians and can be...
spiral 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...
that is estimated to be 23 ± 4 million 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 from the Milky Way Galaxy. 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....
Canes Venatici
Canes Venatici
Canes Venatici is one of the 88 official modern constellations. It is a small northern constellation that was created by Johannes Hevelius in the 17th century. Its name is Latin for "hunting dogs", and the constellation is often depicted in illustrations as representing the dogs of Boötes the...
. It is one of the most famous galaxies in the sky.
The galaxy and its companion (NGC 5195
NGC 5195
NGC 5195 is a dwarf galaxy that is interacting with the Whirlpool Galaxy . Both galaxies are located approximately 25 million light-years away in the constellation Canes Venatici...
) are easily observed by 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...
, and the two galaxies may even be seen with binoculars
Binoculars
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...
. The Whirlpool Galaxy is also a popular target for professional astronomers, who study it to further understand galaxy structure (particularly structure associated with the spiral arms) and galaxy interactions.
Discovery
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"...
, and is designated as M51
Messier object
The 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...
. Its companion galaxy, NGC 5195
NGC 5195
NGC 5195 is a dwarf galaxy that is interacting with the Whirlpool Galaxy . Both galaxies are located approximately 25 million light-years away in the constellation Canes Venatici...
, was discovered in 1781 by 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:...
. It was however not until 1845 that the Whirlpool became the first to be recognized as a spiral. This was achieved by Lord Rosse
William Parsons, 3rd Earl of Rosse
William Parsons, 3rd Earl of Rosse, Knight of the Order of St Patrick was an Irish astronomer who had several telescopes built. His 72-inch telescope "Leviathan", built 1845, was the world's largest telescope until the early 20th century.-Life:He was born in Yorkshire, England, in the city of...
employing a 72-inch (~1.83 m) reflecting telescope which he constructed at Birr Castle
Birr Castle
Birr Castle is a large castle in the town of Birr in County Offaly, Ireland. It is the home of the seventh Earl of Rosse, and as such the residential areas of the castle are not open to the public, though the grounds and gardens of the demesne are publicly accessible.-Ireland's Historic Science...
, Ireland. Sometimes M51 is used to refer to the pair of galaxies, in which case the individual galaxies may be referred to as M51A (NGC 5194) and M51B (NGC 5195).
In 2005 a supernova
Supernova
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...
(SN 2005cs
SN 2005cs
SN 2005cs was a supernova in the Whirlpool Galaxy. It was a type II supernova, discovered by a German amateur astronomer....
) was observed in the Whirlpool Galaxy, peaking at apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
14.
On 31 May 2011 a magnitude 13.5 type II supernova
Type II supernova
A Type II supernova results from the rapid collapse and violent explosion of a massive star. A star must have at least 9 times, and no more than 40–50 times the mass of the Sun for this type of explosion. It is distinguished from other types of supernova by the presence of hydrogen in its spectrum...
(SN 2011dh
SN 2011dh
SN 2011dh is a supernova in the Whirlpool Galaxy . On 31 May 2011 an apparent magnitude 13.5 type II supernova was detected in M51 at coordinates 13:30:05.08 +47:10:11.2. It was discovered by Amédée Riou and confirmed by several sources, including the Palomar Transient Factory...
) was detected in M51 at coordinates 13:30:05.08 +47:10:11.2.
Properties
With the recent SN 2005cs derived estimate of 23 Mly distance, and an angular diameter of roughly 11.2′, it can be inferred that M51's bright circular disk has a radius of about 38,000 light-years. Its massMass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
is estimated to be 160 billion solar masses.
A black hole
Black hole
A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...
, surrounded by a ring of dust, is thought to exist at the heart of the spiral. The dust ring stands almost perpendicular to the relatively flat spiral nebula. A secondary ring crosses the primary ring on a different axis, a phenomenon that is contrary to expectations. A pair of ionization cone
Ionization cone
Ionisation cones are cones of material extending out from spiral galaxies. They are visible because of their emissions which are believed to be from re-emission of photons produced by nuclear activity within the galaxy itself....
s extend from the axis of the main dust ring.
Visual appearance
Located within the constellation Canes VenaticiCanes Venatici
Canes Venatici is one of the 88 official modern constellations. It is a small northern constellation that was created by Johannes Hevelius in the 17th century. Its name is Latin for "hunting dogs", and the constellation is often depicted in illustrations as representing the dogs of Boötes the...
, M51 is found by following the easternmost star of the Big Dipper
Big Dipper
The Plough, also known as the Big Dipper or the Saptarishi , is an asterism of seven stars that has been recognized as a distinct grouping in many cultures from time immemorial...
, Eta Ursae Majoris
Eta Ursae Majoris
Eta Ursae Majoris is a star in the constellation Ursa Major. It has the traditional names Alkaid and Benetnash ....
, and going 3.5° southeast. Its declination is +47°, making it a circumpolar
Circumpolar star
A circumpolar star is a star that, as viewed from a given latitude on Earth, never sets , due to its proximity to one of the celestial poles...
for observers located above 43°N latitude; it reaches high altitudes throughout the northern hemisphere making it an accessible object from the early hours in winter through the end of spring season, after which observation is hindered in lower latitudes.
M51 is visible through binoculars under dark sky conditions
Bortle Dark-Sky Scale
The Bortle Dark-Sky Scale is a nine-level numeric scale that measures the night sky's and stars' brightness of a particular location. It quantifies the astronomical observability of celestial objects and the interference caused by light pollution and skyglow. John E...
and can be resolved in detail with modern amateur telescopes. When seen through a 100 mm telescope the basic outlines of M51 and its companion are visible. Under dark skies, and with a moderate eyepiece through a 150 mm telescope, M51's intrinsic spiral structure can be detected. With larger (>300 mm) instruments under dark sky conditions, the various spiral bands are apparent with HII regions visible, and M51 can be seen to be attached to M51B.
As is usual for galaxies, the true extent of its structure can only be gathered from inspecting photographs; long exposures reveal a large nebula extending beyond the visible circular appearance.
In January 2005 the Hubble Heritage Project
Hubble Heritage Project
The Hubble Heritage Project was founded by a group of astronomers in 1998. The team releases on an almost monthly basis pictures of celestial objects like planets, stars, galaxies and galaxy clusters....
constructed a 11477x7965 pixel composite image (shown in the info box above) of M51 using Hubble's ACS instrument
Advanced Camera for Surveys
The Advanced Camera for Surveys is a third generation axial instrument aboard the Hubble Space Telescope . The initial design and scientific capabilities of ACS were defined by a team based at Johns Hopkins University. ACS was assembled and tested extensively at Ball Aerospace & Technologies Corp...
.
Spiral structure
The very pronounced spiral structure of the Whirlpool Galaxy is believed to be the result of the close interaction between it and its companion galaxy NGC 5195NGC 5195
NGC 5195 is a dwarf galaxy that is interacting with the Whirlpool Galaxy . Both galaxies are located approximately 25 million light-years away in the constellation Canes Venatici...
.
Star formation
Induced spiral structure in the larger galaxy is not the only effect of the interaction. Significant compression of hydrogen gas occurs that leads to the development of starbirth regions. In pictures of M51 these show up as the bright blue 'knots' throughout the spiral arms.Generally speaking, hydrogen gas is the most common component of the interstellar medium
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...
(the vast space between stars and planetary systems in galaxies). It exists primarily in its atomic and molecular form, and forms huge clouds throughout the entire galaxy. When large sources of gravitational pull pass nearby, such as other galaxies, gravitational interactions produce compression (density) waves that sweep through these hydrogen clouds. This causes some regions of the previously diffuse gas to compress into tight pockets of opaque and dense gas, these are dust lanes one so often sees in the spiral arms. In regions where the concentration and density of gas reaches a critical value, further collapse under its own gravitational pull occurs, and stars are born at the center of the collapse, where the gas is compressed so strongly that fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...
initiates.
When this happens, these new-born stars consume huge amounts of gas causing them to expand, shine even hotter, and finally sweep away the surrounding layers of dust and gas by increasing efflux of the stellar wind. The gigantic proportions of the clouds out of which they are born means stars seldom, if ever, are created in isolation. Thus regions of several hot young stars emit sufficient light energy that they can be seen in the high resolution pictures of M51 across millions of lightyears distance.
For an example of such a formation in our own galaxy, see M16, the Eagle Nebula
Eagle Nebula
The Eagle Nebula is a young open cluster of stars in the constellation Serpens, discovered by Jean-Philippe de Cheseaux in 1745-46. Its name derives from its shape which is resemblant of an eagle...
.
Companion
Decades ago, it was not known with certainty whether the companion galaxy NGC 5195 was a true companion, or another galaxy passing at a distance. The advent of radio astronomy and subsequent radio images of M51 unequivocally demonstrated the reality of the interaction.Recent simulations bear out that M51's spiral structure was caused by NGC 5195 passing through the main disk of M51 about 500 to 600 million years ago. In this model, NGC 5195 came from behind M51 through the disk towards the observer and made another disk crossing as recently as 50 to 100 million years ago until it is where we observe it to be now, slightly behind M51.
Galaxy group information
The Whirlpool Galaxy is the brightest galaxy in the M51 GroupM51 Group
The M51 Group is a group of galaxies located in Canes Venatici. The group is named after the brightest galaxy in the group, the Whirlpool Galaxy...
, a small group of galaxies that also includes M63 (the Sunflower Galaxy), NGC 5023
NGC 5023
NGC 5023 is an edge-on spiral galaxy located in the constellation Canes Venatici. It is considered a member of the M51 Group although it is actually relatively isolated from other galaxies. It is approximately 15 kiloparsecs across and contains more than 200 stars with an apparent magnitude of...
, and NGC 5229
NGC 5229
NGC 5229 is an edge-on spiral galaxy located in the constellation Canes Venatici. It is a member of the M51 Group although in reality it is relatively isolated from other galaxies. The galaxy's disc is somewhat warped and appears to consist of a series of interconnected clusters of stars from our...
. This small group may actually be a subclump at the southeast end of a large, elongated group that includes the M101 Group
M101 Group
The M101 Group is a loose group of galaxies located in Ursa Major. The group is named after the brightest galaxy in the group, the Pinwheel Galaxy . Most of the other members of the group are companions of the Pinwheel Galaxy. The group itself is one of many located within the Virgo Supercluster...
and the NGC 5866 Group
NGC 5866 Group
The NGC 5866 Group is a small group of galaxies located in the constellation Draco. The group is named after NGC 5866, the galaxy with the highest apparent magnitude in the group, although some galaxy group catalogs list NGC 5907 as the brightest member....
, although most group identification methods and catalogs identify the three groups as separate entities.
See also
- 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
- NGC 5195NGC 5195NGC 5195 is a dwarf galaxy that is interacting with the Whirlpool Galaxy . Both galaxies are located approximately 25 million light-years away in the constellation Canes Venatici...
– the companion galaxy to NGC 5194 - NGC 5457 – another grand-design spiral galaxy
- M51 in Fiction