Samuel Whitebook

Two faint embers circle each other in the dark so closely that one begins to tear glowing chunks off the other. That is the picture of the system ZTF J1239+8347, caught by the Zwicky Transient Facility telescope.

A sugar cube sits on a saucer next to a cup of hot tea. Drop it in, and it dissolves within minutes. But if you lower it slowly, the sugar melts gradually, releasing its sweetness into the drink. Something similar is happening in two newly discovered stellar pairs, except the sugar is a brown dwarf and the tea is a star.

Two dim stars whirl so close together that one siphons material off the other, like a spoon delicately skimming foam from broth. Astronomers have for the first time calculated the fate of such pairs — ultracool and brown dwarfs, the coldest and dimmest inhabitants of the galaxy. Previously, it was thought that mass exchange between them was impossible: they were too fragile.