Shock-heating of stellar envelopes: A possible common mechanism at the origin of explosions and eruptions in massive stars

Abstract

Observations of transient phenomena in the Universe reveal a spectrum of mass-ejection properties associated with massive stars, covering from Type II/Ib/Ic core-collapse supernovae (SNe) to giant eruptions of Luminous Blue Variables (LBV) and optical transients. Here, we hypothesize that a fraction of these phenomena may have an explosive origin, the distinguishing ingredient being the ratio of the prompt energy release E_dep to the envelope binding energy E_binding. Using one-dimensional one-group radiation hydrodynamics and a set of 10-25Msun, massive-star models, we explore the dynamical response of a stellar envelope subject to a strong, sudden, and deeply-rooted energy release. Following energy deposition, a shock systematically forms, crosses the progenitor envelope on a day timescale, and breaks-out with a signal of hour-to-days duration and a 10^5-10^11 Lsun luminosity. For E_dep > E_binding, full envelope ejection results with a SN-like bolometric luminosity and kinetic energy, modulations being commensurate to the energy deposited and echoing the diversity of Type II-Plateau SNe. For E_dep ~ E_binding, partial envelope ejection results with a small expansion speed, and a more modest but year-long luminosity plateau, reminiscent of LBV eruptions or so-called SN impostors. For E_dep < E_binding, we obtain a "puffed-up" star, secularly relaxing back to thermal equilibrium. In parallel with gravitational collapse and Type II SNe, we argue that the thermonuclear combustion of merely a few 0.01Msun of C/O could power a wide range of explosions/eruptions in loosely-bound massive stars, as those in the 8-12Msun range, or in more massive ones owing to their proximity to the Eddington limit and/or critical rotation.