The Whirlpool Galaxy, also known as Messier 51a, M51a, and NGC 5194, is an interacting grand-design

spiral galaxy Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''Seyfert 2 active galactic nucleus. It lies in the constellation Canes Venatici, and was the first galaxy to be classified as a spiral galaxy. Its distance is 31 million

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 101 ...

s from Earth. The galaxy and its companion,

NGC 5195 NGC 5195 (also known as Messier 51b or M51b) is a dwarf galaxy that is interacting with the Whirlpool Galaxy (also known as M51a or NGC 5194). Both galaxies are located approximately 25 million light-years away in the constellation Canes Venatic ...

, are easily observed by amateur astronomers, and the two galaxies may be seen with

binoculars Binoculars or field glasses are two refracting telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes ( binocular vision) when viewing distant objects. Most binoculars are sized to be hel ...

. The Whirlpool Galaxy has been extensively observed by professional astronomers, who study it to understand galaxy structure (particularly structure associated with the spiral arms) and galaxy interactions.

Discovery

What later became known as the Whirlpool Galaxy was discovered on October 13, 1773, by Charles Messier while hunting for objects that could confuse comet hunters, and was designated in Messier's catalogue as M51. Its companion galaxy,

, was discovered in 1781 by

Pierre Méchain Pierre François André Méchain (; 16 August 1744 – 20 September 1804) 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 Pierre Méchain was bo ...

, although it was not known whether it was interacting or merely another galaxy passing at a distance. In 1845, William Parsons, 3rd Earl of Rosse, employing a

reflecting telescope A reflecting telescope (also called a reflector) is a telescope that uses a single or a combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century by Isaac Newton as an alternati ...

at Birr Castle, Ireland, found that the Whirlpool possessed a spiral structure, the first "nebula" to be known to have one. These "

spiral nebula Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''Edwin Hubble was able to observe Cepheid variables in some of these spiral nebulae, which provided evidence that they were so far away that they must be entirely separate galaxies. The advent of

radio astronomy Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The first detection of radio waves from an astronomical object was in 1933, when Karl Jansky at Bell Telephone Laboratories reported radiation comi ...

and subsequent radio images of M51 unequivocally demonstrated that the Whirlpool and its companion galaxy are indeed interacting. Sometimes the designation 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).

Visual appearance

Deep in the constellation Canes Venatici, M51 is often found by finding the easternmost star of the

Big Dipper The Big Dipper ( US, Canada) or the Plough ( UK, Ireland) is a large asterism consisting of seven bright stars of the constellation Ursa Major; six of them are of second magnitude and one, Megrez (δ), of third magnitude. Four define a "bowl ...

, Eta Ursae Majoris, and going 3.5° southwest. Its declination is, rounded, +47°, making it circumpolar (never setting) for observers above the 43rd parallel north; it reaches a high altitude throughout this hemisphere making it an accessible object from the early hours in November through to the end of May, after which observation is more coincidental in modest latitudes with the risen sun (due to the Sun approaching to and receding from its

right ascension Right ascension (abbreviated RA; symbol ) is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the March equinox to the ( hour circle of the) point in question above the earth. When pai ...

, specifically figuring in Gemini, just to the north). M51 is visible through

under dark sky conditions, and it can be resolved in detail with modern amateur telescopes. When seen through a 100 mm telescope the basic outlines of M51 (limited to 5×6') 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 1984, thanks to the high-speed detector—the so-called image-photon-counting system (IPCS)—developed jointly by the CNRS Laboratoire d'Astronomie Spatiald (L.A.S.-CNRS) and the Observatoire de Haute Provence (O.H.P.) along with the particularly nice seeing offered by the Canada-France-Hawaii-Telescope (C.F.H.T.) 3.60m Cassegrain focus at Mauna Kea summit in Hawaii, Hua et al. detected the double component of the very nucleus of the Whirlpool galaxy. In January 2005 the Hubble Heritage Project constructed a 11,477 × 7,965-pixel composite image (shown in the infobox above) of M51 using Hubble's ACS instrument. The image highlights the galaxy's spiral arms, and shows detail into some of the structures inside the arms. PIA23128-WhirlpoolGalaxy-VariousLight-20190626

PIA23128-WhirlpoolGalaxy-VariousLight-20190626

Properties

The Whirlpool Galaxy lies at a distance of about 31 million light-years from Earth. Based on the 1991 measurement by the Third Reference Catalogue of Bright Galaxies using the D₂₅ isophote at the B-band, the Whirlpool Galaxy has a diameter of . Overall the galaxy is about 88% the size of the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked ey ...

. Its

mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different element ...

is estimated to be 160 billion solar masses, or around 10.3% of the mass of Milky Way Galaxy. A

black hole A black hole is a region of spacetime where gravity is so strong that nothing, including light or other electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts that a sufficiently compact mass can defo ...

, once thought to be surrounded by a ring of dust, but now believed to be partially occluded by dust instead, exists at the heart of the spiral. A pair of

ionization cone Ionization cones are cones of ionized material extending from active galactic nuclei, predominantly observed in type II Seyfert galaxies. They are detected through their emission of electromagnetic radiation in the visible and infrared parts of ...

s extend from the active galactic nucleus.

Spiral structure

The Whirlpool Galaxy has two, very prominent spiral arms that wind clockwise. One arm deviates from a constant angle significantly. The pronounced spiral structure of the Whirlpool Galaxy is believed to be the result of the close interaction between it and its companion galaxy

, which may have passed through the main disk of M51 about 500 to 600 million years ago. In this proposed scenario, 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. In 2015, a study discovered two new tidal features caused by the interaction between the Whirlpool Galaxy and NGC 5195, the "Northeast plume" and the "South plume". The study remarks that a simulation that takes into account only one passage of NGC 5195 into the Whirpool Galaxy will fail to produce an analogue to the Northeast tail. In contrast, the multiple-passage simulations made by Salo and Laurikainen et.al reproduce the northeast plume.

Star formation

The central region of M51 appears to be undergoing a period of enhanced star formation. The present efficiency of star formation, defined as the ratio of mass of new stars to the mass of star-forming gas, is only ~1%, quite comparable to the global value for the Milky Way and other galaxies. It is estimated that the current high rate of star formation can last no more than another 100 million years or so.

Transient events

Three supernovae have been observed in the Whirlpool Galaxy: In 1994,

SN 1994I SN 1994I is a Type Ic supernova discovered on April 2, 1994 in the Whirlpool Galaxy by amateur astronomers Tim Puckett and Jerry Armstrong of the Atlanta Astronomy Club. Type Ic supernova are a rare type of supernova that result from the explosi ...

was observed in the Whirlpool Galaxy. It was classified as type Ic, indicating that its progenitor star was very massive and had already shed much of its mass, and its brightness peaked at

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

12.91. In June 2005 the type II supernova SN 2005cs was observed in the Whirlpool Galaxy, peaking at apparent magnitude 14. On 31 May 2011 a type II supernova was detected in the Whirlpool Galaxy, peaking at magnitude 12.1. This supernova, designated

SN 2011dh SN 2011dh was a supernova in the Whirlpool Galaxy (M51). It was discovered on 31 May 2011, with an apparent magnitude 13.5. and confirmed by several sources, including the Palomar Transient Factory. A candidate progenitor was detected in Hubble ...

, showed a spectrum much bluer than average, with P Cygni profiles, which indicate rapidly expanding material, in its hydrogen-Balmer lines. The progenitor was probably a yellow supergiant and not a red or blue supergiant, which are thought to be the most common supernova progenitors. On 22 January 2019, a supernova impostor, designated

AT2019abn AT or at may refer to: Geography Austria * Austria (ISO 2-letter country code) * .at, Internet country code top-level domain United States * Atchison County, Kansas (county code) * The Appalachian Trail (A.T.), a 2,180+ mile long mountai ...

, was discovered in Messier 51. The transient was later identified as a luminous red nova. The progenitor star was detected in archival Spitzer Space Telescope infrared images. No object could be seen at the position of the transient in archival

Hubble The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...

images, indicating that the progenitor star was heavily obstructed by interstellar dust. 2019abn peaked at magnitude 17, reaching an

intrinsic brightness In science and engineering, an intrinsic property is a Property (philosophy), property of a specified subject that exists itself or within the subject. An extrinsic property is not essential or inherent to the subject that is being characteri ...

M_=-14.9

Planet candidate

In September 2020, the detection by the

Chandra X-ray Observatory The Chandra X-ray Observatory (CXO), previously known as the Advanced X-ray Astrophysics Facility (AXAF), is a Flagship-class space telescope launched aboard the during STS-93 by NASA on July 23, 1999. Chandra is sensitive to X-ray sources ...

of a candidate exoplanet, named

M51-ULS-1b The Whirlpool Galaxy, also known as Messier 51a, M51a, and NGC 5194, is an interacting grand-design spiral galaxy with a Seyfert 2 active galactic nucleus. It lies in the constellation Canes Venatici, and was the first galaxy to be classified ...

, orbiting the high-mass X-ray binary M51-ULS-1 in this galaxy was announced. If confirmed, it would be the first known instance of an extragalactic planet, a planet ''outside'' the

Galaxy. The planet candidate was detected by eclipses of the X-ray source (XRS), which consists of a stellar remnant (either a

neutron star A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes and some hypothetical objects (e.g. w ...

or a

) and a massive star, likely a B-type supergiant. The planet would be slightly smaller than

Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; ...

and orbit at a distance of some tens of

astronomical unit The astronomical unit (symbol: au, or or AU) is a unit of length, roughly the distance from Earth to the Sun and approximately equal to or 8.3 light-minutes. The actual distance from Earth to the Sun varies by about 3% as Earth orbi ...

Companion

(also known as Messier 51b or M51b) is a dwarf galaxy that is interacting with the Whirlpool Galaxy (also known as M51a or NGC 5194). Both galaxies are located approximately 31 million light-years away in the constellation Canes Venatici. Together, the two galaxies are one of the most widely studied interacting galaxy pairs.

Galaxy group information

The Whirlpool Galaxy is the brightest galaxy in the M51 Group, 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.

Gallery

File:M51 whirlpool galaxy black hole.jpg, A 1992 Hubble image showing a knot of dust once thought to be a pair of rings encircling a black hole File:M51 Nucleus ACS WFC F555W.png, A 2005 Hubble image showing details of the dust at the nucleus of M51 File:2019abn NBO 2019-03-12.png, Supernova impostor AT2019abn, imaged at Northolt Branch Observatories in March 2019 File:2019abn-Hubble.png, Supernova impostor AT2019abn, imaged by the

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most ver ...

File:Whirlpool Galaxy M51a.jpg, alt=Taken in 2022 from the UK., Amateur astrophotographer's image taken in 2022 of Whirlpool Galaxy

References and footnotes

External links

StarDate: M51 Fact Sheet

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Whirlpool Galaxy at ESA/Hubble

The Whirlpool Galaxy at Constellation Guide
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The Whirlpool Galaxy in the Staracle Messier catalog
{{DEFAULTSORT:Whirlpool Galaxy Unbarred spiral galaxies Interacting galaxies Peculiar galaxies M51 Group Canes Venatici Messier objects NGC objects 08493 47404 085 Seyfert galaxies 17731013 Discoveries by Charles Messier