Messier 100

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.

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.

Seven supernovae have been identified in M100.^[5]

• In March 1901 the first was found, SN 1901B,^[5][15] a type I supernova found with a magnitude of 15.6 at 110"W and 4"N from its nucleus.
• SN 1914A^[5][16] was then discovered in February to March 1914; its type was undeterminable but was found with a magnitude of 15.7 at 24"E and 111"S from its nucleus.
• Galactic observation from early to mid 1960^[b] found SN 1959E, another type I supernova,^[5][17] with the faintest magnitude, 17.5, among the five found, at 58"E and 21"S from its nucleus.
• On April 15, 1979, the first type II supernova found in the M100 galaxy was discovered; however the star SN 1979C^[5][18] faded quickly; later observations from x-ray to radio wavelengths revealed its remnant.
• The fifth supernova was discovered February 7, 2006; the star SN 2006X^[5][19] had a magnitude of 15.3 when discovered two weeks before fading to magnitude +17.
• Supernova SN 2019ehk, discovered on April 29, 2019, reached a peak magnitude of approximately 15.8.
• The seventh supernova, SN 2020oi, was discovered on January 7, 2020. It was a type Ic supernova, which reached a peak magnitude of 17.7.^[5][20]

• 
  Image of Messier 100 taken by the NASA/ESA Hubble Space Telescope
• 
  Messier 100 Hubble images centered on supernova SN 2019ehk

• List of Messier objects

Wikimedia Commons has media related to Messier 100.

• SEDS: Spiral Galaxy 100
• Messier 100 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images
• ESA/Hubble Messier 100
• NASA Astronomy Picture of the Day