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 as a spiral galaxy. Its distance is estimated to be between 15 and 35 million light-years.
The galaxy and its companion, NGC 5195, are easily observed by amateur astronomers, and the two galaxies may be seen with binoculars. 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.
Whirlpool Galaxy (M51A or NGC 5194), the smaller object in the upper right is M51B or NGC 5195
|Observation data (J2000 epoch)|
|Right ascension||13h 29m 52.7s|
|Declination||+47° 11′ 43″|
|Distance||23 Mly (7.1 ± 1.2 Mpc)|
|Apparent magnitude (V)||8.4|
|Size||~60,000ly in diameter|
|Apparent size (V)||11′.2 × 6′.9|
|Notable features||Interacting with NGC 5195|
|Question Mark Galaxy, Rosse's Galaxy, M51a, NGC 5194, UGC 8493, PGC 47404, VV 001a, VV 403, Arp 85, GC 3572|
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, NGC 5195, was discovered in 1781 by Pierre Méchain, 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 72-inch (1.8 m) reflecting telescope at Birr Castle, Ireland, found the Whirlpool possessed a spiral structure, the first "nebula" to be known to have one. These "spiral nebulae" were not recognized as galaxies until 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 even though they are seen close together .
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).
Located within the constellation Canes Venatici, M51 is found by following the easternmost star of the Big Dipper, Eta Ursae Majoris, and going 3.5° southwest. 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 it can be resolved in detail with modern amateur telescopes. When seen through a 100 mm telescope the basic outlines of M51 (limited to 5x6') 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 11477 × 7965-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.
M51a lies 30 million light years from Earth and has an estimated diameter of 60,000 light years. Overall the galaxy is about 25–33% the size of the Milky Way. Its mass 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 cones extend from the axis of the main dust ring.
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.
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. 
Three supernovae have been observed in the Whirlpool Galaxy. In 1994, SN 1994I 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 12.91.
On 31 May 2011 a type II supernova was detected in the Whirlpool Galaxy, peaking at magnitude 12.1. This supernova, designated SN 2011dh, 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.
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 Venatici. Together, the two galaxies are one of the most widely studied interacting galaxy pairs.
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.
1773 in science
The year 1773 in science and technology involved some significant events.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 Herdsman, a neighboring constellation. Cor Caroli is the constellation's brightest star, with an apparent magnitude of 2.9. La Superba is one of the reddest stars in the sky and one of the brightest carbon stars. The Whirlpool Galaxy is a spiral galaxy tilted face-on to observers on Earth, and was the first galaxy whose spiral nature was discerned.Dianne Bos
Dianne Bos is a Canadian photographer based in Calgary, Alberta, whose works have been exhibited internationally since 1981.
Bos was born in Dundas, Ontario, in 1956. She earned a degree in sculpture from Mount Allison University.Many of Bos' photographs are produced using a homemade pinhole camera. These images are not intended to be an objective record of a particular object or place, but an attempt to capture a memory.Bos participated in the group exhibition, Time & Space curated by Josephine Mills and organized by the University of Lethbridge Art Gallery in 2007. The exhibition toured to the Dunlop Art Gallery, Regina; The Rooms, Newfoundland and Labrador, St. John's; and the Owens Art Gallery, Sackville.For her Galaxies series, Bos experimented with photographing different light sources through multiple pinholes. Her 2001 work M51 by Candlelight depicts the Whirlpool Galaxy and is included in the New Mexico History Museum's Pinhole Resource Collection. She created the image using an aluminum plate camera dotted with dozens of pinholes of varying sizes. A photograph that Bos took in Toulouse was used by graphic designer Jennifer Clark for her mural Timeless.Bos made pinhole cameras from old travel books for an exhibition at Toronto's Edward Day Gallery in 2011. R.M. Vaughan described the photographs as both sleepy and tense, writing that they "replicate those first moments of waking, when tenuous reality comes into semi-focus."In June 2013, her Bowness home was submerged when the Bow River flooded. She lost her collection of homemade pinhole cameras, her darkroom and studio as well as hundreds of printed images.Bos is represented by Edward Day Gallery in Toronto; Jennifer Kostuik Gallery in Vancouver; Newzones in Calgary; and Beaux-arts des Amériques, Montreal.Galaxies in fiction
Galaxies 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 the Milky Way, and in the cases of Andromeda and Triangulum the Local Group's two largest other galaxies. The difficulties involved in crossing the immense distances between galaxies are often overlooked in this type of science fiction.Interacting galaxy
Interacting galaxies (colliding 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, which may lead to a galaxy merger.List of Hubble anniversary images
List of Hubble anniversary images is a list of images released to celebrate the Hubble Space Telescope anniversaries. They celebrate its "birthday" when it was launched into orbit on April 23, 1990 by the Space Shuttle with its crew.List of galaxies named after people
A 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.
Many of the brighter galaxies visible from the Northern Hemisphere have Messier numbers, named after Charles Messier. For instance, the Andromeda Galaxy is Messier 31 and the Whirlpool Galaxy is Messier 51. There are a few other comprehensive catalogs that assign the cataloguer's name to galaxies. For instance, Markarian galaxies, named after Benjamin Markarian, are galaxies with excess blue and ultraviolet emission; galaxies in the Atlas of Peculiar Galaxies are assigned an Arp number after Halton Arp who produced the catalog; etc. Objects in these catalogs are excluded below, except in cases where they carry the name of an additional person.Logarithmic spiral
A logarithmic spiral, equiangular spiral or growth spiral is a self-similar spiral curve which often appears in nature. The logarithmic spiral was first described by Descartes and later extensively investigated by Jacob Bernoulli, who called it Spira mirabilis, "the marvelous spiral".M51 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 (M51A). Other notable members include the companion galaxy to the Whirlpool Galaxy (M51B) and the Sunflower Galaxy (M63).Messier 63
Messier 63 or M63, also known as NGC 5055 or the seldom-used Sunflower Galaxy, is a spiral galaxy in the northern constellation of Canes Venatici. M63 was first discovered by the French astronomer Pierre Méchain then later verified by his colleague Charles Messier on June 14, 1779. The galaxy became listed as object 63 in the Messier Catalogue. In the mid-19th century, Anglo-Irish astronomer Lord Rosse identified spiral structures within the galaxy, making this one of the first galaxies in which such structure was identified.This galaxy has a morphological classification of SAbc, indicating a spiral shape with no central bar feature and moderate to loosely wound arms. There is a general lack of large scale continuous spiral structure in visible light, a galaxy form known as flocculent. However, when observed in the near infrared a symmetric, two-arm structure becomes apparent. Each arm wraps 150° around the galaxy and extends out to 13 kly (4 kpc) from the nucleus.M63 is an active galaxy with a LINER nucleus. This displays as an unresolved nuclear source wrapped in a diffuse emission. The latter is extended along a position angle of 110° and soft X-rays and H-alpha emission can be observed coming from along nearly the same direction. The existence of a super massive black hole (SMBH) at the nucleus is uncertain; if it does exist, then the mass is estimated as (8.5±1.9)×108 M☉.Radio observations at 21-cm show the gaseous disk of M63 extending outward to a radius of 40 kpc (130 kly), well past the bright optical disk. This gas shows a symmetrical form that is warped in a pronounced manner, starting at a radius of 10 kpc (33 kly). The form suggests the dark matter halo of the galaxy is offset with respect to the inner region. The reason for the warp is unclear, but the position angle points toward the smaller companion galaxy, UGC 8313.The distance to M63, based upon the luminosity-distance measurement is 8.99 Mpc (29.3 Mly). The radial velocity relative to the Local Group yields an estimate of 4.65 Mpc (15.2 Mly). Estimates based on the Tully-Fisher relation range over 5.0–10.3 Mpc (16–34 Mly). The tip of the red-giant branch technique gives a distance of 8.87 ± 0.29 Mpc (28.93 ± 0.95 Mly). M63 is part of the M51 Group, a group of galaxies that also includes M51 (the 'Whirlpool Galaxy').In 1971, a supernova with a magnitude of 11.8 appeared in one of the arms of M63. It was discovered May 24, 1971 and reached peak light around May 26. The spectrum of SN 1971 I is consistent with a supernova of type I. However, the spectroscopic behavior appeared anomalous.NGC 2997
NGC 2997 is a face-on unbarred spiral galaxy about 25 million light-years away in the constellation Antlia. It is the brightest galaxy of the NGC 2997 group of galaxies.
NGC 2997 is particularly notable for a nucleus surrounded by a chain of hot giant clouds of ionized hydrogen. It is featured on the cover of the first edition of Galactic Dynamics by James Binney and Scott Tremaine.NGC 406
NGC 406 is a spiral galaxy quite similar to the well known Whirlpool Galaxy, located some 65 million light-years away, in the southern constellation of Tucana (the Toucan) and discovered in 1834 by John Herschel. It is described in the New General Catalogue as "faint, very large, round, very gradually a little brighter middle". NGC 406 is about 60000 light-years across, roughly half the diameter of the Milky way.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 Venatici. Together, the two galaxies are one of the most famous interacting galaxy pairs.NGC 772
NGC 772 (also known as Arp 78) is an unbarred spiral galaxy approximately 130 million light-years away in the constellation Aries.NGC 7752 and NGC 7753
NGC 7752 and NGC 7753 are a pair of galaxies approximately 272 million light-years away in the constellation Pegasus.
NGC 7753 is the primary galaxy. It is a barred spiral galaxy with a small nucleus. NGC 7752 is the satellite galaxy of NGC 7753. It is a barred lenticular galaxy that is apparently attached to one of NGC 7753's spiral arms. They resemble the Whirlpool Galaxy (M51A) and its satellite NGC 5195 (M51B).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 explosion of a very massive star that has shed its outer layers of hydrogen and helium. The explosion results in a highly luminous burst of radiation that then dims over the course of weeks or months. SN 1994I was a relatively nearby supernova, and provided an important addition to the then small collection of known Type Ic supernova. Very early images were captured of SN 1994I, as two high school students in Oil City, Pennsylvania serendipitously took images of the Whirlpool Galaxy using the 30-inch telescope at Leuschner Observatory on March 31, 1994, which included SN 1994I just after it began to brighten.SN 2005cs
SN 2005cs was a supernova in the Whirlpool Galaxy. It was a type II supernova, discovered in 2005 by Wolfgang Kloehr, a German amateur astronomer.SN 2011dh
SN 2011dh is a supernova in the Whirlpool Galaxy (M51). On 31 May 2011 an apparent magnitude 13.5 type II supernova (the explosion of a single massive star) was detected in M51 at coordinates 13:30:05.08 +47:10:11.2. It was discovered by Tom Reiland; Thomas Griga; Amédée Riou; and Stephane Lamotte Bailey and confirmed by several sources, including the Palomar Transient Factory. A candidate progenitor has been detected in Hubble Space Telescope images at coordinates 13:30:05.119 +47:10:11.55. The progenitor may have been a highly luminous yellow supergiant with an initial mass of 18-24 solar masses. The supernova appears to have peaked near apparent magnitude 12.1 on 19 June 2011.Emission spectra from W. M. Keck Observatory, obtained by Palomar Transient Factory indicate that this is a type II supernova with a relatively blue continuum with P Cygni profiles in the Balmer series. This is a unique event, because it occurs in a galaxy that is imaged almost constantly. It is expected to be observable for northern hemisphere observers for several months.This is the third supernova to be recorded in the Whirlpool galaxy in 17 years (following SN 1994I and SN 2005cs) which is a lot for a single galaxy. The galactic supernova frequency is estimated to be around one event every 40 years.Unbarred spiral galaxy
An unbarred spiral galaxy is a type of spiral galaxy without a central bar, or one that is not a barred spiral galaxy. It is designated with an SA in the galaxy morphological classification scheme.
The Sombrero Galaxy is an unbarred spiral galaxy.
Barless spiral galaxies are one of three general types of spiral galaxies under the de Vaucouleurs system classification system, the other two being intermediate spiral galaxy and barred spiral galaxy. Under the Hubble tuning fork, it is one of two general types of spiral galaxy, the other being barred spirals.
New General Catalogue 5000 to 5499
List of notable Seyfert galaxies