Ring Galaxy NGC 922

Bright, pink nebulas almost completely encircle a distorted spiral galaxy in this Hubble Space Telescope image of NGC 922. The ring structure and the galaxy's disturbed shape result from a smaller galaxy scoring a cosmic bull's-eye, hitting the center of NGC 922 some 330 million years ago. The smaller galaxy, named 2MASXI J0224301-244443 and located outside the frame of this image, plunged through the heart of NGC 922 and emerged out the other side. As the smaller galaxy passed through the middle of NGC 922, it set up gravitational ripples that disrupted the clouds of gas and triggered the formation of new stars whose radiation then lit up the remaining gas. The bright pink color of the resulting nebulae is a characteristic sign of this process and is caused by glowing hydrogen gas (the dominant element in interstellar gas clouds).