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]

• 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 (type Ib, mag. 16.5) on 29 April 2019. The supernova reached a peak magnitude of approximately 15.8.^[25]
• SN 2020oi (type Ic, mag. 17.28) was discovered by Automatic Learning for the Rapid Classification of Events (ALeRCE) on 7 January 2020.^[5][26][27]

• List of Messier objects

• 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