M 100 

Messier 100 (M 100, NGC 4321) is a grand design intermediate spiral galaxy in the southern part of the mildly northern Coma Berenices. It is one of the brightest and largest galaxies in the Virgo Cluster and is approximately 55 million light-years from our galaxy, and about 166,000 light-years in diameter. It was discovered by Pierre Méchain in 1781 and 29 days later seen again and entered by Charles Messier in his catalogue "of nebulae and star clusters". M 100 was one of the first spiral galaxies to be discovered,  and was listed as one of fourteen spiral nebulae by Lord William Parsons of Rosse in 1850. 

NGC 4322 and NGC 4328 are satellite galaxies of M 100; the former is connected with it by a bridge of luminous matter.

Messier 100 is considered a starburst galaxy 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: 1000  parsecs – where star formation has been taking place for at least 500 million years in separate bursts.