Arp 220

The massive galaxy Arp 220 is in fact two galaxies colliding into one, with large scale star formation taking place. Arp 220 has more than 200 mammoth star clusters which have as many as 10 million suns, twice as massive as any comparable star clusters in the Milky Way Galaxy. The clusters are so compact, however, that even at their moderate distance they look like brilliant single stars.

Observations have revealed two populations of star clusters in the galaxy. One population is less than 10 million years old; the second, 70 to 500 million years old. Clusters in the younger group are more massive than those in the older group.

The star birth frenzy is happening in a very small region, about 5000 LY across, where the gas and dust is very dense. There is as much gas in that tiny region as there is in the entire Milky Way Galaxy.