In a star cluster, like on a crowded dance floor, massive stars rarely stay single. More often they whirl in pairs or triples, and the distance between them can be less than from Earth to the Sun. But how do they manage to get so close to each other?

Simulations showed: it's all about the disk of gas and dust that envelops the pair. This disk, like a drain funnel, swirls the stars and slowly pulls them inward. In the first hundred thousand years, a blink of an eye by cosmic standards, the distance between the stars can shrink by a factor of a thousand.

Such a close encounter does not go unnoticed. The stars may merge, forming more massive luminaries, and sometimes — black holes or neutron stars. These compact objects later become sources of X-ray radiation that telescopes detect.

So tight pairs of massive stars are not a coincidence but a natural outcome of the work of gas and dust disks.