Messier 100 (also known as NGC 4321 or the Mirror Galaxy) is a grand design intermediate spiral galaxy in the southern part of the mildly northern

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 ...

. It is one of the brightest and largest galaxies in the

Virgo Cluster The Virgo Cluster is a cluster of galaxies whose center is 53.8 ± 0.3 Mly (16.5 ± 0.1 Mpc) away in the Virgo constellation. Comprising approximately 1,300 (and possibly up to 2,000) member galaxies, the cluster forms the heart of the larger ...

and is approximately 55 million

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s from our galaxy, about 166,000 light-years in diameter. 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 ...

in 1781 and 29 days later seen again and entered by

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 ...

in his catalogue "of nebulae and star clusters". It was one of the first spiral galaxies to be discovered, and was listed as one of fourteen

spiral nebulae Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''

by Lord William Parsons of Rosse in 1850. NGC 4323 and NGC 4328 are

satellite galaxies A satellite galaxy is a smaller companion galaxy that travels on bound orbits within the gravitational potential of a more massive and Luminosity, luminous host galaxy (also known as the primary galaxy). Satellite galaxies and their constituents ...

of M100; the former is connected with it by a bridge of luminous matter.

Early observations

After the discovery of M100 by Méchain,

made observations of the galaxy depicting it as a nebula without a

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

. He pointed out that it was difficult to recognize the

nebula A nebula (; or nebulas) is a distinct luminescent part of interstellar medium, which can consist of ionized, neutral, or molecular hydrogen and also cosmic dust. Nebulae are often star-forming regions, such as in the Pillars of Creation in ...

because of its faintness.

William Herschel Frederick William Herschel ( ; ; 15 November 1738 – 25 August 1822) was a German-British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline Herschel. Born in the Electorate of Hanover ...

was able to identify a bright cluster of stars within the "nebula" during his observations. His son

John John is a common English name and surname: * John (given name) * John (surname) John may also refer to: New Testament Works * Gospel of John, a title often shortened to John * First Epistle of John, often shortened to 1 John * Second E ...

expanded the findings in 1833. With the advent of better telescopes, John Herschel was able to see a round, brighter galaxy; however, he also mentioned that it was barely visible through clouds. William Henry Smyth extended the studies of M100, detailing it as a pearly white nebula and pointing out diffuse spots.

Star formation

Messier 100 is considered 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 ...

with the strongest

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 concentrated in its center, within a ring – actually two tightly wound

spiral arm Spiral arms are a defining feature of spiral galaxies. They manifest as spiral-shaped regions of enhanced brightness within the galactic disc. Typically, spiral galaxies exhibit two or more spiral arms. The collective configuration of these arms i ...

s attached to a small nuclear bar of radius: one thousand

parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (AU), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and ...

s – where

has been taking place for at least 500 million years in separate bursts. As usual on spiral galaxies of the Virgo Cluster, in the rest of the disk both star formation and neutral hydrogen, of which M100 is deficient compared to isolated spiral galaxies of similar Hubble type, are truncated within the galaxy's disk, which is caused by interactions with the intracluster medium of Virgo.

Supernovae

Seven

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

e have been identified in M100: * On 17 March 1901

Heber Curtis Heber Doust Curtis (June 27, 1872 – January 9, 1942) was an American astronomer. He participated in 11 expeditions for the study of solar eclipses, and, as an advocate and theorist that additional galaxies existed outside of the Milky Way, wa ...

discovered SN 1901B ( type I, mag. 15.6), at 110"W and 4"N from the galaxy's nucleus. * Heber Curtis discovered SN 1914A (type unknown, mag. 15.7) on 2 March 1914, at 24"E and 111"S from the galaxy's nucleus. *

Milton Humason Milton La Salle Humason (August 19, 1891 – June 18, 1972) was an American astronomer. He worked with Edwin Hubble to measure the redshift of nebulas in the early 20th century, providing evidence of the expansion of the universe. Biography ...

, with observations from early to mid 1960, discovered SN 1959E (type I, mag. 17.5), located 58"E and 21"S from the galaxy's nucleus. * On 15 April 1979, amateur astronomer Gus Johnson discovered SN 1979C, the first

type II supernova A Type II supernova or SNII (plural: ''supernovae'') results from the rapid collapse and violent explosion of a massive star. A star must have at least eight times, but no more than 40 to 50 times, the mass of the Sun () to undergo this type ...

found in the M100 galaxy. However, the star faded quickly, and later observations from x-ray to radio wavelengths revealed its remnant. * SN 2006X (type Ia, mag. 15.3) was discovered by Shoji Suzuki and Marco Migliardi on 7 February 2006, two weeks before fading to magnitude 17. * Jaroslaw Grzegorzek discovered SN 2019ehk ( typeIb, mag. 16.5) on 29 April 2019. The supernova reached a peak magnitude of approximately 15.8. * SN 2020oi ( typeIc, mag. 17.28) was discovered by ''Automatic Learning for the Rapid Classification of Events'' (ALeRCE) on 7 January 2020.

References and footnotes

External links

SEDS: Spiral Galaxy 100
*
ESA/Hubble Messier 100

{{DEFAULTSORT:Messier 100 Messier 100 Intermediate spiral galaxies Coma Berenices 100 NGC objects 17810413 Virgo Cluster Discoveries by Pierre Méchain 07450 +03-32-015 12204+1605 040153

Early observations

Star formation

Supernovae

See also

References and footnotes

External links