The Zwicky Transient Facility has begun to discover binary systems with orbital periods that are less than 1 hr .
Combined with dedicated follow-up systems , which allow for high-cadence photometry of these sources , systematic confirmation and characterization of these sources are now possible .
Here , we report the discovery of ZTF J190125.42+530929.5 , a 40.6 min orbital period , eclipsing double white-dwarf binary .
Both photometric and spectroscopic modeling confirm its nature , yielding an estimated inclination of i = 86.2 ^ { +0.6 } _ { -0.2 } degrees and primary and secondary effective temperatures of \textrm { T } _ { \textrm { eff } } = 28 , 000 ^ { +500 } _ { -500 } K and \textrm { T } _ { \textrm { eff } } = 17 , 600 ^ { +400 } _ { -400 } K respectively .
This system adds to a growing list of sources for future gravitational-wave detectors and contributes to the demographic analysis of double degenerates .