ZTF J1813+4251

ZTF J1813+4251 is a binary star system including a star and white dwarf, co-orbiting every 51 minutes, about 3,000 light years away in the constellation of Hercules. It is considered a cataclysmic variable with the white dwarf pulling outer layers of hydrogen from the star onto itself. It has the shortest orbital period of all hydrogen-rich cataclysmic variable stars known. It is predicted that the orbital period will reach a minimum of 18 minutes within 75 million years as the system evolves.

It was identified in 2022 by Kevin Burdge of MIT using a computer algorithm that searched over 1,000 images from the Zwicky Transient Facility, identifying stars that had brightness variability periods around one hour.