We have good reasons to think that Luminous Red Novae (LRNe) signal the merger of two stars. But what powers the light curves of the brightest extragalactic events? Using radiation transport module developed by Diego Calderón for moving-mesh code JET by Paul Duffell we performed 2D simulations of LRNe powered by shock interaction with a “disky” structure left behind by pre-merger processes. Compared to homologously expanding spheres, shock-powered events are a factor of ~10 brighter and can be about twice as long. Amazing to see how the shock feeds the energy to the rest of the ejecta for reprocessing, while remaining hidden inside. But the photosphere is not spherical and can dramatically change shape if the shock encounters a well-defined outer edge of the CSM, like what can be seen in the raytraced images in the movie below. Signs of this might be found in spectral line profiles and/or polarimetry.
Other issues considered: hydrogen+helium equation of state, tabulated opacites, low effective temperatures, dust formation, irradiation by the central merger remnant.
Accepted to ApJL, this work marks the end of my ERC StG that finished in the summer but I hope it is also just a beginning on the path of making LRNe useful probes of binary evolution!
https://arxiv.org/abs/2508.09257