Long Wang

Double neutron stars are pairs of ultra-dense remnants of exploded massive stars. They orbit each other and gradually spiral closer until they merge in a powerful flash — a source of gravitational waves. But where do such pairs actually form? One possibility is inside star clusters, where stars are plentiful and interact closely.

At the center of attention are tiny stellar cities: ultra-faint dwarf galaxies. They resemble sparse swarms of fireflies circling within a vast invisible cloud. This cloud is a halo of ultralight dark matter. Its particles are so light that they behave not like billiard balls but like waves.