Галактика Водоворот в созвездии Гончих Псов

Galaxy in the constellation Canes Venatici
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 and its pair with NGC 5195 to understand galaxy structure (particularly structure associated with the 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.

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. William Parsons, 3rd Earl of Rosse, employing a reflecting telescope at Birr Castle, Ireland, found that 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. 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).

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 (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, specifically figuring in 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. 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.

The Whirlpool Galaxy lies at a distance of about 23 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 Its mass is estimated to be 160 billion solar masses, or around 10.3% of the mass of Milky Way Galaxy. 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 cones extend from the active galactic nucleus.

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 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.

As a result of the Whirpool 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 from the galaxy's center. This plume is uniform in color and likely originated from the Whirpool 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. In contrast, the multiple passage simulations made by Salo and Laurikainen et. al reproduce the northeast plume. Similarly, the spiral arms are experiencing high levels of star formation, as well as the space along the arms.

In September 2020, the detection by the Chandra X ray Observatory of a 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 Galaxy. The planet candidate was detected by eclipses of the 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 supergiant. The planet would be slightly smaller than Saturn and orbit at a distance of some tens of astronomical units.

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 31 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.