Interacting Galaxies NGC 3921

Astronomers now recognize that today’s large galaxies, particularly elliptical ones, were formed from the merger of smaller galactic systems. The pair of interacting disk galaxies pictured here — known as NGC 3921 — is one of these mergers seen in its late stages. Observations show that both of the galaxies involved were roughly the same mass and collided about 700 million years ago. You can see clearly in this image the disturbed morphology, tails and loops characteristic of a post-merger. The clash of galaxies caused a rush of star formation, and previous Hubble observations showed over a thousand bright, young star clusters bursting to life at the heart of the galaxy pair.