astronomyforamateurs: Ring galaxies are thought to be the result of a collision between two galaxies

astronomyforamateurs:

Ring galaxies are thought to be the result of a collision between two galaxies of different sizes. When a smaller galaxy passes through the disk of a larger one, the increased gravitational interaction condenses the gas and dust clouds at the center of the galaxy and creates a “shock wave” that sends star forming regions away from the point of collision. In the case of the galaxy system Arp 147, two separate ring galaxies were created in the collision. 

Credit: M Livio et al. (STScI), ESA, NASA

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