Messier 99 or M99, also known as NGC 4254 or St. Catherine's Wheel, is a

grand design spiral galaxy A grand design spiral galaxy is a spiral galaxy with prominent and well-defined continuous spiral arms, as opposed to multi-arm, patchy and flocculent spirals which have subtler structural features. The spiral arms of a grand design galaxy exten ...

in the northern

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Coma Berenices Coma Berenices is an ancient asterism in the northern sky, which has been defined as one of the 88 modern constellations. It is in the direction of the fourth galactic quadrant, between Leo and Boötes, and it is visible in both hemispher ...

approximately from the

Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

. It was discovered 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 ...

on 17 March 1781. The discovery was then reported to

Charles Messier Charles Messier (; 26 June 1730 – 12 April 1817) was a French astronomer. He published an astronomical catalogue consisting of 110 nebulae and star clusters, which came to be known as the ''Messier objects'', referred to with th ...

, who included the object in the

Messier Catalogue The Messier objects are a set of 110 astronomical objects catalogued by the French astronomer Charles Messier in his ' (''Catalogue of Nebulae and Star Clusters''). Because Messier was interested only in finding comets, he created a list of thos ...

of comet-like objects. It was one of the first galaxies in which a spiral pattern was seen. This pattern was first identified by Lord Rosse in the spring of 1846. This galaxy has a morphological classification of SA(s)c, indicating a pure spiral shape with loosely wound

arms Arms or ARMS may refer to: *Arm or arms, the upper limbs of the body Arm, Arms, or ARMS may also refer to: People * Ida A. T. Arms (1856–1931), American missionary-educator, temperance leader Coat of arms or weapons *Armaments or weapons **Fi ...

. It has a peculiar shape with one normal looking arm and an extended arm that is less tightly wound. The galaxy is inclined by 42° to the line-of-sight with a major axis

position angle In astronomy, position angle (usually abbreviated PA) is the convention for measuring angles on the sky. The International Astronomical Union defines it as the angle measured relative to the Celestial pole, north celestial pole (NCP), turning pos ...

of 68°. A bridge of neutral hydrogen gas links NGC 4254 with

VIRGOHI21 VIRGOHI21 is an extended region of neutral hydrogen (HI) in the Virgo cluster discovered in 2005. Analysis of its internal motion indicates that it may contain a large amount of dark matter, as much as a small galaxy. Since VIRGOHI21 apparently c ...

, an HI region and a possible

dark galaxy A dark galaxy is a hypothesized galaxy with no (or very few) stars. They received their name because they have no visible stars but may be detectable if they contain significant amounts of gas. Astronomers have long theorized the existence of dark ...

. The gravity from the latter may have distorted M99 and drawn out the gas bridge, as the two galaxy-sized objects may have had a close encounter before parting greatly. However, VIRGOHI21 may instead be tidal debris from an interaction with the

lenticular galaxy A lenticular galaxy (denoted S0) is a Galaxy morphological classification, type of galaxy intermediate between an elliptical galaxy, elliptical (denoted E) and a spiral galaxy in galaxy morphological classification schemes. It contains a large-s ...

NGC 4262 some 280 million years ago. It is expected that the drawn out arm will relax to match the normal arm once the encounter is over. While not classified as a

starburst galaxy A starburst galaxy is one undergoing an exceptionally high rate of star formation, as compared to the long-term average rate of star formation in the galaxy, or the star formation rate observed in most other galaxies. For example, the star format ...

, M99 has a

star formation Star formation is the process by which dense regions within molecular clouds in interstellar space—sometimes referred to as "stellar nurseries" or "star-forming regions"—Jeans instability, collapse and form stars. As a branch of astronomy, sta ...

activity three times larger than other galaxies of similar

Hubble type The Hubble sequence is a morphological classification scheme for galaxies published by Edwin Hubble in 1926. It is often colloquially known as the Hubble tuning-fork diagram because the shape in which it is traditionally represented resembles a t ...

that may have been triggered by the encounter. M99 is likely entering the Virgo Cluster for the first time bound to the periphery of the cluster at a projected separation of 3.7°, or around one megaparsec, from the cluster center at

Messier 87 Messier 87 (also known as Virgo A or NGC 4486, generally abbreviated to M87) is a Type-cD galaxy, supergiant elliptical galaxy, elliptical galaxy in the constellation Virgo (constellation), Virgo that contains several trillion s ...

. The galaxy is undergoing

ram-pressure stripping Ram pressure is a pressure exerted on a body moving through a fluid medium, caused by relative bulk motion of the fluid rather than random thermal motion. It causes a drag force to be exerted on the body. Ram pressure is given in tensor form as ...

of much of its

interstellar medium The interstellar medium (ISM) is the matter and radiation that exists in the outer space, space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as cosmic dust, dust and cosmic rays. It f ...

as it moves through the

intracluster medium In astronomy, the intracluster medium (ICM) is the superheated plasma (physics), plasma that permeates a galaxy cluster. The gas consists mainly of ionized hydrogen and helium and accounts for most of the baryonic material in galaxy clusters. The ...

Supernovae

Four

supernovae A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion. The original ob ...

have been observed in M99: * SN 1967H ( type II, mag. 14.0) was discovered by

Fritz Zwicky Fritz Zwicky (; ; February 14, 1898 – February 8, 1974) was a Swiss astronomer. He worked most of his life at the California Institute of Technology in the United States of America, where he made many important contributions in theoretical an ...

on 1 July 1967. * SN 1972Q (type unknown, mag. 15.8) was discovered by Leonida Rosino on 14 December 1972. * SN 1986I (type II, mag. 14) was discovered by Carlton Pennypacker et al. on 17 May 1986. * SN 2014L ( type Ic, mag. 17.2) was discovered by the THU-NAOC Transient Survey (TNTS) on 26 January 2014. __NOTOC__

References

External links

SEDS: Spiral Galaxy M99

PPARC: New evidence for a Dark Matter Galaxy
* * {{DEFAULTSORT:Messier 99 Unbarred spiral galaxies Messier 099 Messier 099 099 Messier 099 07345 39578 17810317 Discoveries by Pierre Méchain

Supernovae

See also

References

External links