rotation axis

460 light-years away, around the star HD 135344B, a dense disk of gas and dust is swirling. It looks like a giant vinyl record that someone has cracked: a gap yawns in the disk, and across it, like a slender bridge, stretches a dust filament.

An octopus tentacle bends, grabs, and stretches — all without a single bone. The secret is that inside it, sections that contract alternate with sections that remain passive. Scientists have long tried to replicate this trick in artificial materials, but until now they couldn't precisely dictate how a material would change shape. Now researchers have proposed 3D-printing elastic threads from two materials at once.

An ordinary top spun on a table slows down smoothly: friction with the air and the surface gradually eats away its energy. But if a top levitates in a magnetic field and barely touches anything, its rotation can behave surprisingly capriciously.

At the edge of spacetime, where all light rays end, live symmetries that physicists have debated for half a century. They are called superrotations, transformations of the celestial sphere that diverge at isolated points, like vortices in superfluid helium.