When Galaxies Collide - July 9, 2001
Hubble’s face-on view of this unusual galaxy, known as Hoag’s Object after Arthur Allen Hoag, who discovered it in 1950, shows its nearly perfect ring of hot, massive, blue stars surrounding a nucleus of older, yellow stars. Ring-shaped galaxies can form either through a collision with another galaxy or when a second galaxy speeds through the first, leaving parts of itself behind. In Hoag's Object, there is evidence that the blue ring may be the shredded remains of a galaxy that passed nearby. Astronomers estimate that the encounter occurred 2 billion to 3 billion years ago.