Illuminating binary evolution with Luminous Red Novae, their progenitors, and their dusty aftermath

Abstract: Binary stellar interactions create a wide range of high-impact astrophysical phenomena, including novae, supernovae, X-ray binaries, and gravitational-wave sources. A key open problem is how initially wide binaries evolve into the compact systems required to produce these outcomes. This orbital shrinkage is thought to occur during common envelope (CE) evolution, a brief but dramatic phase of unstable mass transfer during which the envelope of the donor gets ejected by the inspiraling companion star. While full ejections leave a compact binary, partial ejections end up in mergers. Over the past two decades, the CE evolution has been linked to a class of optical transients known as Luminous Red Novae (LRNe), which are routinely discovered by ongoing time-domain surveys. Studies of LRNe and their progenitors reveal that the onset of envelope ejection is often preceded by a complex sequence of mass-transfer episodes. For the most energetic events, shocks and interaction with previously ejected material dominate the observed luminosity and the event’s extended duration. Following the outburst, the ejecta cools in a matter of weeks, forming substantial amounts of molecules and dust. Recent dust-mass estimates with the James Webb Space Telescope (JWST) suggest that LRNe may significantly contribute to the missing ISM dust reservoir, comparable to core-collapse supernovae. In this talk, I will discuss how observations of LRNe and their dusty remnants are reshaping our understanding of binary evolution. I will present what lessons we have learned so far and what the next steps are within the current time-domain landscape.