THREE'S COMPANY

Galaxy pair Arp-Madore 2339-661 is actually a galaxy trio

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HUBBLE SPACE TELESCOPE, 23 OCTOBER 2023

Individually, the two galaxies in this image - which lie 500 million lightyears from Earth in the constellation of Tucana - are known as NGC 7734 (top left) and NGC 7733 (bottom right). Collectively, they're known as Arp-Madore 2339-661, the moniker given to them when they were described in the Arp-Madore catalogue of peculiar galaxies, which was compiled in the 1970s and '80s.

A closer look, though, reveals that the two galaxies are actually three. Roughly two-thirds of the way along the blue upper arm of NGC 7733, you can see what appears to be a small clump of brown matter. Astronomers now believe that this is a third galaxy, provisionally now referred to as NGC 7733N. As the three galaxies are in very close proximity to one another, scientists say they will eventually merge to become one.