After the discovery of M100 by Méchain, Charles Messier made observations of the galaxy depicting it as a nebula without a star. He pointed out that it was difficult[7] to recognize the nebula because of its faintness. William Herschel was able to identify a bright cluster of stars[7] within the "nebula" during his observations. His son John 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[7] 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[10] with the strongest star formation activity concentrated in its center, within a ring – actually two tightly wound spiral arms attached to a small nuclear bar of radius: one thousand parsecs[11] – where star formation has been taking place for at least 500 million years in separate bursts.[12]
As usual on spiral galaxies of the Virgo Cluster, in the rest of the disk both star formation[13] and neutral hydrogen, of which M100 is deficient compared to isolated spiral galaxies of similar Hubble type,[14] are truncated within the galaxy's disk, which is caused by interactions with the intracluster medium of Virgo.
On 17 March 1901 Heber Curtis discovered SN 1901B (type I, mag. 15.6),[5][15] at 110"W and 4"N from the galaxy's nucleus.[16]
Heber Curtis discovered SN 1914A (type unknown, mag. 15.7)[5][17] on 2 March 1914, at 24"E and 111"S from the galaxy's nucleus.[16]
Milton Humason, with observations from early to mid 1960,[b] discovered SN 1959E (type I, mag. 17.5),[5][18] located 58"E and 21"S from the galaxy's nucleus.[19]
On 15 April 1979, amateur astronomer Gus Johnson discovered SN 1979C, the first type II supernova found in the M100 galaxy. However, the star faded quickly, and later observations from x-ray to radio wavelengths revealed its remnant.[5][20][21]
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.[5][22][23][24]
Jaroslaw Grzegorzek discovered SN 2019ehk (typeIb, mag. 16.5) on 29 April 2019. The supernova reached a peak magnitude of approximately 15.8.[25]
SN 2020oi (typeIc, mag. 17.28) was discovered by Automatic Learning for the Rapid Classification of Events (ALeRCE) on 7 January 2020.[5][26][27]
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Wozniak, H.; Friedli, D.; Martinet, L.; Pfenniger, D. (1999). "Double-barred starburst galaxies viewed by ISOCAM". The Universe as Seen by ISO. 427: 989. Bibcode:1999ESASP.427..989W.
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Sakamoto, Kazushi; Okumura, Sachiko; Minezaki, Takeo; Kobayashi, Yukiyasu; et al. (1995). "Bar-Driven Gas Structure and Star Formation in the Center of M100". The Astronomical Journal. 110 (3): 2075. Bibcode:1995AJ....110.2075S. doi:10.1086/117670.
