2024RNAAS...8..323M

Using the Zwicky Transient Facility (ZTF), Burdge et al. discovered systems of eclipsing double white dwarfs (EDWDs) having orbital periods < 1 hr. From the properties of 3 of the discovered systems, I estimate a merger rate of DWDs, per unit stellar mass in the Galaxy, of R_merge,M* ≈ 4.8 × 10^–13 yr${}^{-1}\,{M}_{\odot }^{-1}$. This likely somewhat underestimates the rate, because of several known effects that work against EDWD detection in ZTF. The derived merger rate is within the uncertainty range, R_merge,M* = (4.6-5.8) × 10^–13 yr${}^{-1}\,{M}_{\odot }^{-1}$, measured independently by Maoz et al. based on two samples of DWDs discovered via radial-velocity variations. Based on the expected period distribution of DWDs and their detectability, of order 100 additional EDWDs with periods > 1 hr are discoverable in ZTF, with potential to significantly improve the merger-rate's measurement precision.