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 with a radius of 1 kilo-parsec - where star formation has been taking place since at least 500 million years ago in separate bursts .
Messier 100 is considered a starburst galaxy with a radius of 1 kilo-parsec , where star formation has been taking place for least 500 million years in separate bursts .