Arp 4 is a galactic duo immortalized by the Hubble Space Telescope. In the image, a small bright spiral appears to be orbiting around a larger, darker companion. However, this apparent proximity ...

The universe contains roughly 18 galaxies for every person on Earth. With such profusion, is there any reason why any of them should particularly catch our notice? Halton Arp had the answer. Born in ...

American astronomer Halton Christian Arp passed away in Munich, Germany, on December 28. He was 86. Arp was a world-renowned expert on interacting and merging galaxies. His 1966 book Atlas of Peculiar ...

Colliding galaxies may be common, but cosmic cacophony on this scale is still unusual. What we have here are two galaxies merging together in your standard collision…and then a third galaxy sidling in ...