Galaxies possess gravitational forces that can slowly pull close objects toward them. More massive galaxies have stronger gravitational forces. In this picture, the strong gravitational forces of the heftier galaxy, NGC 2207, lock both objects in an orbital embrace. These galaxies are the closest they've been in 40 million years. They are destined to continue swirling around each other, slowly falling closer together until the two become one beefy galaxy.
Spiral galaxies contain large concentrations of gas and dust.
A merger between two spirals condenses the gas clouds, igniting star birth. Astronomers believe that many of today's galaxies, including the Milky Way, were assembled in the same way. The galaxies in this image reside 114 million light-years from Earth in the direction of the constellation Canis Major.