View source for Whirlpool Galaxy

{{Short description|Galaxy in the constellation Canes Venatici}}
{{redirect|Galaxy M51|the smartphone|Samsung Galaxy M51}}
{{Infobox galaxy
| name               = Whirlpool Galaxy
| image              = File:Messier51 sRGB.jpg
| caption            = Whirlpool Galaxy (M51a), as taken by the [[European Space Agency]], the smaller object in the upper right is [[NGC 5195]] (M51b)<br />([[NASA]]/[[European Space Agency|ESA]])
| epoch              = [[Epoch (astronomy)#Julian years and J2000|J2000.0]]
| constellation name = [[Canes Venatici]]<ref name="sinnott1988">
{{cite book
 | first=J. L. E. |last=Dreyer | authorlink = John Louis Emil 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|13|29|52.7}}<ref name="ned"/>
| dec                = {{DEC|+47|11|43}}<ref name="ned"/>
| z                  = {{val|0.001534|0.000007}}<ref name="ned"/>
| dist_ly            = {{convert|7.22|+/-|2.13|Mpc|e6ly|sigfig=3|abbr=off|lk=on}}<br />
<ref name=ned/><ref>{{Cite web|url=https://www.nasa.gov/feature/goddard/2017/messier-51-the-whirlpool-galaxy|title = Messier 51 (The Whirlpool Galaxy)|date = 6 October 2017}}</ref>
<br />
| appmag_v           = 8.4<ref name="SEDS">{{cite web |url=http://messier.seds.org/m/m051.html |publisher=SEDS.org |title=M51 }}</ref>
| type               = SA(s)bc pec<ref name="ned">{{cite web
 | title=NASA/IPAC Extragalactic Database
 | work=Results for NGC 5194
 | url=https://ned.ipac.caltech.edu/cgi-bin/objsearch?objname=NGC+5194&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=2006-12-06 |df=mdy-all
}}</ref>
| size = {{cvt|23.58|kpc|ly|sigfig=3|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 | authorlink = Gérard de Vaucouleurs | first2=Antoinette | authorlink2 = Antoinette de Vaucouleurs | last3=Corwin | first3=Herold G. | last4=Buta | first4=Ronald J. | last5=Paturel | first5=Georges | last6=Fouque | first6=Pascal }}</ref>
| size_v             = {{val|11.2|x|6.9|ul=arcminute}}<ref name="ned"/>
| notes              = Interacting with [[NGC 5195]]<ref name="arp1966"/>
| names              = Question Mark Galaxy,<ref name="ned"/> Rosse's Galaxy,<ref name="ned"/> [[Messier object|M]]51a,<ref name="ned"/> [[New General Catalogue|NGC]] 5194,<ref name="ned"/> [[Uppsala General Catalogue|UGC]] 8493,<ref name="ned"/> [[Principal Galaxies Catalogue|PGC]] 47404,<ref name="ned"/> VV 001a,<ref name="ned"/> VV 403,<ref name="ned"/> [[Atlas of Peculiar Galaxies|Arp]] 85,<ref name="ned"/> [[Boss General Catalogue|GC]] 3572<ref name="ned"/>
}}

The '''Whirlpool Galaxy''', also known as '''Messier 51a''' ('''M51a''') or '''NGC 5194''', is an [[Interacting galaxy|interacting]] [[grand design spiral galaxy|grand-design]] [[spiral galaxy]] with a [[Seyfert galaxy|Seyfert 2]] [[active galactic nucleus]].<ref name="arp1966">{{cite journal
 | first1=D. M. | last1=Elmegreen | author-link1=Debra Elmegreen
 | first2=B. G. | last2=Elmegreen | author-link2=Bruce Elmegreen
 | date=1987
 | title=Arm classifications for spiral galaxies
 | journal=[[Astrophysical Journal]]
 | volume=314 | pages=3–9
 | bibcode=1987ApJ...314....3E
 | doi=10.1086/165034
}}</ref><ref name="elmegreenelmegreen1987">
{{cite journal
 | first=H. |last=Arp | authorlink = Halton Arp
 | date=1966
 | title=Atlas of Peculiar Galaxies
 | journal=[[Astrophysical Journal Supplement]]
 | volume=14 | pages=1
 | bibcode=1966ApJS...14....1A
 | doi=10.1086/190147
}}</ref><ref name=A>{{cite journal |last1=Matsushita|first1=Satoki |last2=Muller|first2=Sebastien |last3=Lim|first3=Jeremy |date=9 April 2007 |title=Jet-disturbed molecular gas near the Seyfert 2 nucleus in M51 |journal= Astronomy & Astrophysics |volume= 468 |issue=A&A Letters Special Issue |pages= L49–L52 |doi=10.1051/0004-6361:20067039 |arxiv=0704.0947 |bibcode=2007A&A...468L..49M |s2cid=15471799}}</ref> It lies in the [[constellation]] [[Canes Venatici]], and was the first galaxy to be classified as a spiral galaxy.<ref>{{cite web |title=Whirlpool Galaxy: First Spiral Galaxy |url=http://www.universeforfacts.com/2012/04/whirlpool-galaxy-first-spiral-galaxy.html |website=Universe for Facts |access-date=2014-12-21}}</ref> It is 31 million lightyears (9.5 megaparsecs/Mpc) away and {{convert|23.58|kpc|ly|sigfig=3}} in diameter.<ref name=ned/><ref>{{cite web |last=Garner |first=Rob |date=2017-10-06 |title=Messier 51 (The Whirlpool Galaxy) |url=http://www.nasa.gov/feature/goddard/2017/messier-51-the-whirlpool-galaxy |access-date=2021-01-20 |publisher=NASA |quote=Discovered by Charles Messier in 1773, M51 is located 31 million light-years from Earth in the constellation Canes Venatici.}}</ref>

The galaxy and its companion, [[NGC 5195]],<ref>{{cite web |website=Messier Objects 101.com |url=https://messierobjects101.com/messier-object-m51/ |title=M 51 |date=2016-10-10 |archive-date=2016-10-28 |url-status=dead |archive-url=https://web.archive.org/web/20161028023934/https://messierobjects101.com/messier-object-m51/ }}</ref> are easily observed by [[Amateur astronomy|amateur astronomers]], and the two galaxies may be seen with [[binoculars]].<ref name=apod>{{cite APOD |date=2013-02-24 |title=M51: The Whirlpool Galaxy |access-date=2018-10-11 |df=mdy-all}}</ref> The Whirlpool Galaxy has been extensively observed by professional astronomers, who study it and its pair with dwarf galaxy NGC 5195 to understand galaxy structure (particularly structure associated with the [[Spiral galaxy#Spiral arms|spiral arms]]) and galaxy interactions. Its pair with NGC 5195 is among the most famous and relatively close interacting systems, and thus is a favorite subject of galaxy interaction models.

==Discovery==
[[File:M51Sketch.jpg|thumb|left|Sketch of M51 by [[William Parsons, 3rd Earl of Rosse|Lord Rosse]] in 1845]]

<ref>
{{cite book
 |first=Charles |last=Messier
 |date=1781
 |chapter=[[Catalogue des Nébuleuses & des amas d'Étoiles]]
 |title=Connaissance des Temps [1784]
 |pages=227–267 [246]
}}</ref> [[William Parsons, 3rd Earl of Rosse]], employing a {{Convert|72|in|m|adj=on}} [[reflecting telescope]] at [[Birr Castle]], Ireland, found that the Whirlpool possessed a [[Spiral galaxy|spiral structure]], the first "nebula" to be known to have one.<ref>Rosse revealed the spiral structure of Whirlpool galaxy (M51) at the 1845 meeting of the British Association for the Advancement of Science. Rosse's illustration of M51 was reproduced in J.P. Nichol's book of 1846.
* {{cite journal |last1=Rosse |first1=Earl of |title=On the nebula 25 Herschel, or 61 [should read: 51] of Messier's catalogue |journal=Report of the Fifteenth Meeting of the British Association for the Advancement of Science; Held at Cambridge in June 1845 § Notices and Abstracts of Miscellaneous Communications to the Sections |series=Report of the ... Meeting of the British Association for the Advancement of Science (1833) |date=1846 |page=4 |url=https://babel.hathitrust.org/cgi/pt?id=njp.32101049356890&view=1up&seq=402 }}
* {{cite book |last1=Nichol |first1=John Pringle | authorlink = John Pringle Nichol |title=Thoughts on Some Important Points Relating to the System of the World |date=1846 |publisher=William Tait |location=Edinburgh, Scotland |page=23 |url=https://babel.hathitrust.org/cgi/pt?id=uc2.ark:/13960/t9k360k8b&view=1up&seq=65 }} Rosse's illustration of the Whirlpool galaxy appears on the plate that immediately precedes p. 23.</ref> These "[[spiral nebula]]e" were not recognized as galaxies until [[Edwin Hubble]] was able to observe [[Cepheid variable]]s in some of these spiral nebulae, which provided evidence that they were so far away that they must be entirely separate galaxies. 
The Whirlpool Galaxy was discovered on October 13, 1773, by [[Charles Messier]] while searching for objects that might confuse comet hunters. It was later cataloged as M51 in [[Messier object|Messier's]] list of astronomical objects.<ref>
{{cite journal
 |last1=Hubble |first1=E. P.
 |date=1929
 |title=A spiral nebula as a stellar system, Messier 31
 |journal=[[Astrophysical Journal]]
 |volume=69 |pages=103–158
 |bibcode=1929ApJ....69..103H
 |doi=10.1086/143167
 |doi-access=free
 }}</ref>

The advent of [[radio astronomy]] 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==
[[File:The Two-faced Whirlpool Galaxy.jpg|thumb|The image of the Whirlpool Galaxy in visible light (left) and infrared light (right)]]

Deep in the constellation [[Canes Venatici]], M51 is often found by finding the easternmost star of the [[Big Dipper]], [[Alkaid]], and going 3.5° southwest. Its declination is, rounded, +47°, making it [[Circumpolar star|circumpolar]] (never setting) for observers above the [[43rd parallel north]];{{efn|47 out of 90 degrees north of the [[celestial equator]]. Thus its light emits as far south, to a good minimal cumulation of 15° above the horizon, once a day, on the [[28th parallel south]].}} 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]], specifically figuring in [[Gemini (constellation)|Gemini]], just to the north).

M51 is visible through [[binoculars]] under dark sky conditions, and it can be resolved in detail with modern amateur telescopes.<ref name="apod"/> When seen through a 100&nbsp;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&nbsp;mm telescope, M51's intrinsic spiral structure can be detected. With larger (>300&nbsp;mm) instruments under dark sky conditions, the various spiral bands are apparent with [[HII region]]s 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 visibility offered by the Canada-France-Hawaii-Telescope (C.F.H.T.) 3.60m Cassegrain focus on the summit of Mauna Kea in Hawaii, Hua et al. detected the double component of the very nucleus of the Whirlpool Galaxy.<ref>{{Cite journal |last1=Hua |display-authors=etal |date=1987 |title=[Unknown] |journal=Astrophysical Letters & Communications |volume=25 |number=<!--poss 3--> |issn=0888-6512 |oclc=60627567 |pages=187–204 }}</ref>{{Full citation needed|date=October 2021}}

In January 2005 the [[Hubble Heritage Project]] constructed a 11,477&nbsp;×&nbsp;7,965-pixel composite image (shown in the infobox above) of M51 using Hubble's [[Advanced Camera for Surveys|ACS instrument]]. The image highlights the galaxy's spiral arms, and shows detail into some of the structures inside the arms.<ref>{{Cite web |title=Hubble Celebrates 15th Anniversary with Spectacular New Images |url=https://hubblesite.org/contents/news-releases/2005/news-2005-12.html |department=News Center |publisher=[[HubbleSite]] |date=April 25, 2005 |access-date=13 October 2024}}</ref>

[[File:PIA23128-WhirlpoolGalaxy-VariousLight-20190626.jpg|thumb|center|500px|<div align="center">Whirlpool Galaxy – Observed in Various Light<br/>{{small|a) 0.4 and 0.7 μm; b) vis-blue/green and IR-red; c) 3.6, 4.5, and 8 μm; d) 24 μm <!---(June 26, 2019)--->}}</div>]]

==Properties==
[[File:M51 whirlpool galaxy black hole.jpg|thumb|A 1992 Hubble image showing M51's active galactic nucleus, occluded by some dust]]The Whirlpool Galaxy lies at a distance of 23<ref name="ned" /> to 31 million light-years from Earth.<ref>{{Cite web |url= https://www.nasa.gov/feature/goddard/2017/messier-51-the-whirlpool-galaxy |title= Hubble's Messier Catalogue – Messier 51 (The Whirlpool Galaxy) |date=2017-10-17 |publisher=NASA |language=en |access-date=2021-09-06|df=mdy-all}}</ref> Based on the 1991 measurement by the Third Reference Catalogue of Bright Galaxies using the [[Galaxy#Isophotal diameter|D<sub>25</sub> isophote]] at the B-band, the Whirlpool Galaxy has a diameter of {{convert|23.58|kpc|ly|sigfig=3|abbr=off|lk=on}}.<ref name="ned" /><ref name="RC3" /> Overall the galaxy is about 88% the size of the [[Milky Way]].<ref name="Average">{{cite arXiv |eprint=astro-ph/9704216 |title=The Milky Way is just an average spiral | date=22 April 1997|last1=Goodwin |first1=S. P. |last2=Gribbin |first2=J. | authorlink2 = John Gribbin |last3=Hendry |first3=M. A. }}</ref><ref name="Goodwin">{{cite journal |last1=Goodwin |first1=S. P. |last2=Gribbin |first2=J. |last3=Hendry |first3=M. A. |date=August 1998 |title=The relative size of the Milky Way |bibcode=1998Obs...118..201G |journal=The Observatory |volume=118 |pages=201–208 }}</ref><ref name="Castro">{{cite journal |arxiv=astro-ph/0205553|doi=10.1051/0004-6361:20020895 |title=Warps and correlations with intrinsic parameters of galaxies in the visible and radio |year=2002 |last1=Castro-Rodríguez |first1=N. |last2=López-Corredoira |first2=M. |last3=Sánchez-Saavedra |first3=M. L. |last4=Battaner |first4=E. |journal=Astronomy & Astrophysics |volume=391 |issue=2 |pages=519–530 |bibcode=2002A&A...391..519C |s2cid=17813024 }}</ref> Its [[mass]] is estimated to be 160 billion solar masses,<ref>{{Cite web |url=http://herschel.cf.ac.uk/results/whirlpool-galaxy |title=Whirlpool Galaxy |date=2009-06-19 |website=Herschel Space Observatory |publisher=Cardiff University |language=en |access-date=2018-10-11 |df=mdy-all |archive-date=2019-01-10 |archive-url=https://web.archive.org/web/20190110061926/http://herschel.cf.ac.uk/results/whirlpool-galaxy |url-status=dead }}</ref> or around 10.3% of the mass of Milky Way Galaxy. It's believed to be an estimated 400 million years old.

A [[black hole]], 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]]s extend from the active galactic nucleus.<ref>{{cite web | date=June 8, 1992 | url=http://hubblesite.org/newscenter/newsdesk/archive/releases/1992/17/text/ | title=NASA's Hubble Space Telescope Resolves a Dark "x" Across the Nucleus of M51 | work=News Center | publisher=HubbleSite | access-date=August 7, 2006 }}</ref>

===Spiral structure===
The Whirlpool Galaxy has two, very prominent spiral arms that wind clockwise. One arm deviates from a constant angle significantly. <ref name="structure">{{cite journal |last1=Honig |first1=Z.N. |last2=Reid |first2=M.J. |title=Characteristics of Spiral Arms in Late-type Galaxies |journal=The Astrophysical Journal |date=February 2015 |volume=800 |issue=1 |pages=5387–5394 |doi=10.1088/0004-637X/800/1/53 |pmid=53 |arxiv=1412.1012 |bibcode=2015ApJ...800...53H |s2cid=118666575 |url=https://ui.adsabs.harvard.edu/abs/2015ApJ...800...53H/abstract |access-date=November 10, 2022}}</ref> The pronounced spiral structure of the Whirlpool Galaxy is believed to be the result of the close interaction between it and its companion galaxy NGC 5195, 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.<ref name="Salo & Laurikainen">
{{cite journal
 | last1=Salo |first1=Heikki |last2=Laurikainen |first2=Eija
 | date=1999
 | title=A Multiple Encounter Model of M51
 | journal=[[Astrophysics and Space Science]]
 | volume=269 | pages=663–664
 | bibcode=1999Ap&SS.269..663S
 | doi=10.1023/A:1017002909665
|s2cid=189838328 }}</ref>

===Tidal features===
As a result of the Whirlpool Galaxy's interaction with NGC 5195, a variety of tidal features have been created. The largest of these features is the so-called Northwest plume, which extends out to {{convert|43|kpc|ly|sigfig=3|abbr=off|lk=on}} from the galaxy's center. This plume is uniform in color and likely originated from the Whirlpool Galaxy itself due to having diffuse gas. Adjacent to it are two other plumes that have a slightly bluer color, referred to as the Western plumes due to their location.<ref name=watkinsM51/>

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 Whirlpool Galaxy will fail to produce an analogue to the Northeast tail.<ref name="watkinsM51">{{cite journal |last1=Watkins |first1=Aaron E. |last2=Mihos |first2=J. Christopher |last3=Harding |first3=Paul |title=Deep Imaging of M51: a New View of the Whirlpool's Extended Tidal Debris |journal=The Astrophysical Journal |date=February 2015 |volume=800 |issue=1 |pages=7 |doi=10.1088/2041-8205/800/1/L3 |arxiv=1501.04599 |bibcode=2015ApJ...800L...3W |s2cid=118603790 |url=https://ui.adsabs.harvard.edu/abs/2015ApJ...800L...3W/abstract |access-date=November 18, 2022}}</ref> In contrast, the multiple-passage simulations made by Salo and Laurikainen et.al reproduce the northeast plume. <ref name="Salo & Laurikainen" /><ref name="watkinsM51"/>

===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.<ref name="Thronson & Greenhouse">
{{cite journal
 | last1=Thronson |first1=Harley A. |last2=Greenhouse |first2=Matthew A.
 | date=1988
 | title=Near-Infrared Mass-to-light ratios in Galaxies: Stellar Mass and Star Formation in the Heart of the Whirlpool
 | journal=[[The Astrophysical Journal]]
 | volume=327 | pages=671–679
 |bibcode=1988ApJ...327..671T |doi = 10.1086/166224 | doi-access=free }}</ref>
Similarly, the spiral arms are experiencing high levels of star formation, as well as the space along the arms.<ref name="Starformation-efficiency M51">{{cite journal |last1=Knapen |first1=Johan H. |last2=Beckman |first2=John E. |last3=Cepa |first3=Jordi |last4=van der Hulst |first4=Thijs |last5=Rand |first5=Richard J. |title=Star Formation Efficiency Patterns in the Spiral Arms of M51 |journal=Astrophysical Journal Letters |date=February 1992 |volume=385 |pages=4 |doi=10.1086/186272 |bibcode=1992ApJ...385L..37K |doi-access=free }}</ref>

===Transient events===
Three [[supernova]]e have been observed in the Whirlpool Galaxy:<ref>{{cite web | url=http://www.cbat.eps.harvard.edu/lists/Supernovae.html | title=List of Supernovae | publisher=Central Bureau for Astronomical Telegrams | access-date=February 27, 2016}}</ref>

In 1994, [[SN 1994I]] was observed in the Whirlpool Galaxy. It was classified as [[Type Ic supernova|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]] 12.91.<ref>{{cite journal | title = The properties of the 'standard' Type Ic supernova 1994I from spectral models | display-authors = 4 | author = Sauer, D. N. | author2 = Mazzali, P. A. | author3 = Deng, J. | author4 = Valenti, S. | author5 = Nomoto, K. | author6 = Filippenko, A. V. | journal = [[Monthly Notices of the Royal Astronomical Society]] | volume = 369 | issue = 4 | pages = 1939–1948 | date = 2006 | doi = 10.1111/j.1365-2966.2006.10438.x | doi-access = free | bibcode = 2006MNRAS.369.1939S|arxiv = astro-ph/0604293 | s2cid = 119510845 }}</ref>

In June 2005 the type II supernova [[SN 2005cs]] was observed in the Whirlpool Galaxy, peaking at apparent magnitude 14.<ref>{{cite web | last=MacRobert | first=Alan M. | date=August 24, 2005 | url=http://skyandtelescope.com/news/article_1544_1.asp | title=Supernova in M51 | work=Sky Tonight | publisher=Sky and Telescope | access-date=August 7, 2006 }}</ref><ref>{{cite web | last=Bishop | first=David | url=http://www.supernovae.net/sn2005/sn2005cs.html | title=Supernova 2005cs in M51 | work=supernovae.net | access-date=August 7, 2006 | url-status=dead | archive-url=https://web.archive.org/web/20061003010723/http://www.supernovae.net/sn2005/sn2005cs.html | archive-date=October 3, 2006 }}</ref>

On 31 May 2011 a [[type II supernova]] was detected in the Whirlpool Galaxy, peaking at magnitude 12.1.<ref name="supernovae.net">{{cite web
 |title=Supernovae 2011dh in M51
 |publisher=supernovae.net (International Supernovae Network)
 |first=David |last=Bishop
 |url=http://www.rochesterastronomy.org/sn2011/sn2011dh.html
 |access-date=2011-06-06 }}</ref> This supernova, designated [[SN 2011dh]], showed a spectrum much bluer than average, with [[P Cygni]] profiles, which indicate rapidly expanding material, in its [[Balmer series|hydrogen-Balmer lines]].<ref name="AAVSO">{{cite web
 |date=2011-06-03
 |title=AAVSO Special Notice #241: New Supernova in M51
 |publisher=[[American Association of Variable Star Observers|AAVSO]]
 |first=Richard |last=Kinne (kqr)
 |url=http://www.aavso.org/aavso-special-notice-241
 |access-date=2011-06-06 }}</ref> The progenitor was probably a [[yellow supergiant]]<ref name="atel3401">{{cite web
 |date=2011-06-03
 |title=ATEL 3401: Properties of the Candidate Progenitor of SN 2011dh in M51
 |publisher=Astronomers Telegram |url=http://www.astronomerstelegram.org/?read=3401
 |access-date=2011-06-06 }}</ref> and not a [[Red supergiant|red]] or [[blue supergiant]], which are thought to be the most common supernova progenitors.

[[File:2019abn-Hubble.png|thumb|Supernova impostor AT2019abn, imaged by the [[Hubble Space Telescope]]]]

On 22 January 2019, a [[supernova impostor]], designated [[AT 2019abn]], was discovered in Messier 51.<ref>{{cite web | website=Transient Name Server | title=AT{{nbsp}}2019abn| url=https://www.wis-tns.org/object/2019abn | publisher = [[International_Astronomical_Union|IAU]] | access-date=24 August 2024}}</ref> 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 Space Telescope|Hubble]] images, indicating that the progenitor star was heavily obstructed by [[interstellar dust]]. 2019abn peaked at magnitude 17, reaching an [[absolute magnitude|intrinsic brightness]] of <math>M_{r}=-14.9</math>.<ref>{{Cite journal|arxiv=1904.07857|title=Discovery of an intermediate-luminosity red transient in M51 and its likely dust-obscured, infrared-variable progenitor|author1=Jacob E. Jencson|author2=Scott M. Adams|author3=Howard E. Bond|doi=10.3847/2041-8213/ab2c05|journal=The Astrophysical Journal Letters|volume=880|year=2019|issue=L20|pages = L20|bibcode = 2019ApJ...880L..20J|s2cid=119110002 |doi-access=free }}</ref>

===Planet candidate===
In September 2020, the detection by the [[Chandra X-ray Observatory]]<ref>{{Cite news|date=2021-10-25|title=Signs of first planet found outside our galaxy|language=en-GB|work=BBC News|url=https://www.bbc.com/news/science-environment-59044650 |archive-url=https://web.archive.org/web/20211025214850/https://www.bbc.com/news/science-environment-59044650 |archive-date=2021-10-25 |url-status=live}}</ref> of a [[Exoplanet#Candidate discoveries|candidate exoplanet]], named '''M51-ULS-1b''', 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 [[Milky Way]]. The planet candidate was detected by [[Transit (astronomy)|eclipses]] of the [[Astrophysical X-ray source|X-ray source]] (XRS), which consists of a stellar remnant (either a [[neutron star]] or a [[black hole]]) and a massive star, likely a [[B-type star|B-type]] [[Blue supergiant star|supergiant]]. The planet would be slightly smaller than [[Saturn]] and orbit at a distance of some tens of [[astronomical unit]]s.<ref name="NS-20200923">{{cite news |last=Crane |first=Leah |title=Astronomers may have found the first planet in another galaxy |url=https://www.newscientist.com/article/2255431-astronomers-may-have-found-the-first-planet-in-another-galaxy/ |date=23 September 2020 |work=[[New Scientist]] |access-date=25 September 2020 }}</ref><ref>{{Cite journal|last1=Di Stefano|first1=Rosanne|last2=Berndtsson|first2=Julia|last3=Urquhart|first3=Ryan|last4=Soria|first4=Roberto|last5=Kashyap|first5=Vinay L.|last6=Carmichael|first6=Theron W.|last7=Imara|first7=Nia | authorlink7 = Nia Imara |date=2021-10-25|title=A possible planet candidate in an external galaxy detected through X-ray transit|url=https://www.nature.com/articles/s41550-021-01495-w|journal=Nature Astronomy|volume=5 |issue=12 |pages=1297–1307 |language=en|arxiv=2009.08987|doi=10.1038/s41550-021-01495-w|bibcode=2021NatAs...5.1297D |s2cid=239892362 |issn=2397-3366}}</ref>

==Companion==
{{main article|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 found in the constellation Canes Venatici, some 31 million light-years away. These two galaxies are among the most extensively researched pairs of interacting galaxies.

==Galaxy group information==
{{main article|M51 Group}}

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]].<ref name="nbg">
{{cite book
 | first=R. B. |last=Tully | authorlink = R. Brent Tully
 | date=1988
 | title=Nearby Galaxies Catalog
 | publisher=[[Cambridge University Press]]
 | isbn=978-0-521-35299-4
}}</ref><ref name="fouqueetal1992">
{{cite journal
 | first1=P. |last1=Fouque |first2=E. |last2=Gourgoulhon |first3=P. |last3=Chamaraux |first4=G. |last4=Paturel
 | date=1992
 | title=Groups of galaxies within 80 Mpc. II - The catalogue of groups and group members
 | journal=[[Astronomy and Astrophysics Supplement]]
 | volume=93 | pages=211–233
 | bibcode=1992A&AS...93..211F
}}</ref><ref name="garcia1993">
{{cite journal
 | first=A. |last=Garcia
 | date=1993
 | title=General study of group membership. II – Determination of nearby groups
 | journal=[[Astronomy and Astrophysics Supplement]]
 | volume=100 | pages=47–90
 | bibcode=1993A&AS..100...47G
}}</ref><ref name="giuricinetal2002">
{{cite journal
 | first1=G. |last1=Giuricin |first2=C. |last2=Marinoni |first3=L. |last3=Ceriani |first4=A. |last4=Pisani
 | date=2000
 | title=Nearby Optical Galaxies: Selection of the Sample and Identification of Groups
 | journal=[[Astrophysical Journal]]
 | volume=543
 | issue=1 | pages=178–194
 | bibcode=2000ApJ...543..178G
 | doi=10.1086/317070
 | arxiv=astro-ph/0001140 |s2cid=9618325 }}</ref> 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.<ref name="ferrareseetal00">
{{cite journal
 | first1=L. |last1=Ferrarese |first2=H. C. |display-authors=4 |last2=Ford |first3=J. |last3=Huchra | authorlink3 = John Huchra |first4=R. C. |last4=Kennicutt Jr. | authorlink4 = Robert Kennicutt |first5=J. R. |last5=Mould |first6=S. |last6=Sakai |first7=W. L. |last7=Freedman |first8=P. B. |last8=Stetson |first9=B. F. |last9=Madore |first10=B. K. |last10=Gibson |first11=J. A. |last11=Graham |first12=S. M. |last12=Hughes |first13=G. D. |last13=Illingworth |first14=D. D. |last14=Kelson |first15=L. |last15=Macri |first16=K. |last16=Sebo |first17=N. A. |last17=Silbermann
 | date=2000
 | title=A Database of Cepheid Distance Moduli and Tip of the Red Giant Branch, Globular Cluster Luminosity Function, Planetary Nebula Luminosity Function, and Surface Brightness Fluctuation Data Useful for Distance Determinations
 | journal=[[Astrophysical Journal Supplement]]
 | volume=128
 | issue=2 | pages=431–459
 | bibcode=2000ApJS..128..431F
 | doi=10.1086/313391
 | arxiv=astro-ph/9910501 |s2cid=121612286 }}</ref>

==See also==
{{Portal|Astronomy|Stars|Outer space}}
* [[Pinwheel Galaxy|Messier 101]] – another grand-design spiral galaxy
* [[List of galaxies]]
* [[List of Messier objects]]

==Notes==
{{Notelist}}

==References==
{{Reflist}}

== External links ==
{{Commons category|Whirlpool Galaxy}}
* [http://www.messier.seds.org/m/m051.html SEDS: Spiral Galaxy M51]
* {{APOD|date=10 April 2001|title=M51: The Whirlpool Galaxy in Dust and Stars}}
* [https://esahubble.org/images/?search=5194 Whirlpool Galaxy at ESA/Hubble]
* [http://ryutao.main.jp/english/st2k_m51_brc.html The Whirlpool Galaxy (Messier 51(a)/NGC 5194)]
* [https://astrobackyard.com/m51-whirlpool-galaxy/ The Whirlpool Galaxy (M51)]
* [http://www.dsi-astronomie.de/M51AO8.html M51 The Whirlpool Galaxy]
* [http://www.constellation-guide.com/whirlpool-galaxy-messier-51/ The Whirlpool Galaxy at Constellation Guide]{{WikiSky|name=The Whirlpool Galaxy}}

{{Catalogs|M=51|NGC=5194|UGC=8493|PGC=47404|VV=403|Arp=85|GC=3572}} {{Sky|13|29|52.7|+|47|11|43|23400000}}
{{Messier objects}}
{{Ngc55}}
{{List of Seyfert galaxies}}
{{Canes Venatici}}

{{DEFAULTSORT:Whirlpool Galaxy}}
[[Category:Arp objects|085]]
[[Category:Astronomical objects discovered in 1773|17731013]]
[[Category:Canes Venatici]]
[[Category:Discoveries by Charles Messier]]
[[Category:Interacting galaxies]]
[[Category:M51 Group]]
[[Category:Messier objects]]
[[Category:NGC objects]]
[[Category:Peculiar galaxies]]
[[Category:Principal Galaxies Catalogue objects|47404]]
[[Category:Seyfert galaxies]]
[[Category:UGC objects|08493]]
[[Category:Unbarred spiral galaxies]]