Marco Gullieuszik

A galaxy plunges into a dense cluster like a runner into a crowd. The oncoming gas, known as the intracluster medium, strips away its own gas, stretching it into a long, glowing tail. Astronomers call these galaxies jellyfish: they have a body and flowing tentacles of stripped material. But only in a few do new stars ignite within those tentacles.

At night, a telescope looks at a star but sees it as a quivering blob. Earth's atmosphere is constantly rippling, and light passing through it bends like a flashlight beam through water.