An Ultra-hot Low-mass Brown Dwarf Eclipsing the Puffy White Dwarf J0404+1112

Most exoplanets known orbit stars that will evolve into red giants, then white dwarfs (WDs). Understanding the population of substellar WD companions informs the common-envelope evolution process (E. Villaver & M. Livio 2009), thereby shedding light on the current and future planetary population of the Milky Way. Here, we report the discovery of a low-mass (25 ± 5 M Jup ) brown dwarf (BD) fully eclipsing every 2.93 hr the WD J0404+1112, which we found to be an unexpectedly large host WD (2 R Earth ). The eclipsing nature of the system, the low masses of the primary (∼0.3 M Sun ) and secondary, and the large day–night temperature contrast for the BD ( ⪭ 2000 K) make it a prime target amongst the dozen WD+BD systems known for a detailed study via JWST phase-curve observations.