English: Artistic illustration of ZTF J1239+8347, an extremely tight binary brown dwarf system that is undergoing mass transfer. This illustration was hand-drawn using Krita and mostly takes inspiration from Robert Hurt's 3D rendering of the system used in the 2026 Caltech press release, with extra changes for better scientific accuracy.

This illustration depicts the process of binary mass transfer, where the more massive component (the accretor) directly pulls material from the less massive component (the donor). Material pulled from the donor is concentrated into a narrow stream of gas that flows directly into the accretor's atmosphere, heating up to a very high temperature of 8900 K and creating a bright blue hotspot in the accretor's atmosphere. The hotspot is much hotter than the accretor's equilibrium temperature of 1500 K; this extreme temperature difference may generate strong winds that would smear the hotspot over the accretor's equator (based on Caltech press release).

Due to the extremely small separation between the components (center-to-center separation of ~170,000 km according to Kepler's 3rd law), both are tidally deformed into teardrop shapes pointing toward each other. In addition, both components orbit and rotate extremely quickly with a period of 57.41 minutes, which further deforms them into oblate teardrops (oblateness ~10%).

Both components are L-type brown dwarfs, having temperatures a bit above 1000 K. This temperature makes them glow orange-red in visible wavelengths, though the slightly hotter accretor glows slightly more orange (ignoring its bright blue hotspot). Due to their extremely fast rotation, the components' atmospheres are highly turbulent and extremely windy, dominated by numerous bands over their latitudes. Numerous convection cells and vortices are depicted on their poles, inspired by brown dwarf atmosphere simulations by Showman et al. (2021).

Due to the highly oblate shapes of the brown dwarfs, internal light is blocked out by their thicker equators, resulting in a darker and more opaque equator (gravity darkening). The gravity darkening effect is depicted for the donor but not for the accretor, whose equator glows bright blue to yellow due to the hotspot being smeared across the accretor's equator via strong zonal winds.