ZTF data from 2018 to 2025 support a decreasing period for J0722−1839 under a fixed eclipse model

We test the orbital clock of the known double white dwarf ZTF J0722−1839. Public ZTF data give 673 g and r detections from 2018 to 2025. The model keeps eclipse profiles fixed with time. It fits one clock and separate flux levels for each year and filter. At BJD TDB 2459600.0, the local period change is −3.13 × 10⁻¹² seconds per second. A changing clock reduces the weighted squared error by 25.52 against a fitted constant period. The 95% interval from 1,000 resamples of 30-day blocks is −4.84 to −1.63 × 10⁻¹² seconds per second. None of 1,000 constant-clock simulations gives an equally large error decrease. The tail fraction with a plus-one correction is 0.001. Both filters and all eight fits that omit one year give negative estimates. Separate eclipse depths by year and cuts to deeper images weaken the evidence. Internal checks with earlier and later data give smaller errors for a changing clock. Those choices followed the full-data pilot. The scale agrees with the circular gravitational-radiation estimate from published masses. The physical cause is not established. The interval applies to the retained detections and fixed profiles. Missing observations and profile changes can affect the result. The package contains frozen public data, audits, code, results, figures, and instructions for repeat analysis.

ZTF J0722-1839 · double white dwarf · eclipsing binary · orbital period change · ZTF DR24 · photometric timing · gravitational radiation · public astronomy data · reproducible research