M 51 (M51A, NGC 5194, PGC 47404, Whirlpool Galaxy) is a spiral galaxy in the constellation Canis Hounds, discovered in 1773 by Charles Messier; the first galaxy to be found to have a spiral structure. It is part of the M51 group of galaxies.
The apparent magnitude of the galaxy is 8.4m; at the end of one of its spiral arms is the companion galaxy NGC 5195. M 51 is quite famous for its pronounced spiral structure and the fact that it is clearly visible even in small telescopes.
M 51 is a spiral galaxy, according to de Vaucouleur's morphological classification, belonging to the SA (s) bc type and having an ordered structure. It belongs to the Seyfert type II galaxies, and also, due to the interaction with the companion NGC 5195, to the peculiar galaxies and is included in the Atlas of Peculiar Galaxies.
The mass of the galaxy is 160 billion solar masses. Estimates of the distance to it differ: there are values in the range of 23 ± 4 to 37 million light years. Estimates of its size also vary: as a rule, its diameter is considered equal to 60-90 thousand light years - thus, the galaxy is several times smaller and less massive than the Milky Way.
The galaxy has an active core that houses a massive black hole. The nucleus has jets, and in the optical and radio ranges it emits more strongly than in the Milky Way, but still much weaker than in most Seyfert galaxies.
Interaction with other galaxies
M 51 has a companion galaxy NGC 5195, which is 2-3 times less massive than M 51 and has a diameter of about 20 thousand light years. The galaxies move in a hyperbolic orbit, their closest approach occurred 900 million years ago at a distance of 16 kiloparsecs (52 thousand light years). Now NGC 5915 is located 147 kiloparsecs (480 thousand light years) further than M 51, and is moving almost in the direction of the line of sight. Due to the gravitational interaction with the companion, a burst of star formation occurs in M 51. The star formation rate is five times higher than normal for such a galaxy, and it is believed that the outburst will last no more than 100 million years.
The Whirlpool Galaxy belongs to the small group of galaxies M51, along with its companion and 6 other galaxies: NGC 5023, UG