A seven-Earth-radius helium-burning star inside a 20.5-min detached binary
Nature Astronomy, Published online: 09 February 2024; doi:10.1038/s41550-023-02188-2 A very uncommon detached binary system with a 20.5-min orbital period has been discovered to harbour a carbon–oxygen white dwarf star and a low-mass subdwarf B star with a seven-Earth radius that