These two galaxies are being drawn toward each other by their mutual gravitational pull. As they interact, stars, gas, and dust are dragged out and the galaxies' shapes become warped.
Surprisingly, when two galaxies collide, the stars within them rarely hit each other, because there is so much empty space between each star. But the tumult and chaos of the collision gives many merging galaxies some of the highest rates of new star formation.
In October, 2007, the Hubble Space Telescope took this image of a pair of galaxies collectively called Arp 87, approximately 300 million light-years away.