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

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. In this work, we hypothesize that a large 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 -25 M_solar 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 time-scale of a day and breaks out with a signal of a duration of hours to days and a 10⁵ -10¹¹ L_solar luminosity. We identify three different regimes, corresponding to a transition from dynamic to quasi-static diffusion transport. For E_dep > E_binding, full envelope ejection results with an 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 thermonuclear combustion, for example of as little as a few 0.01 M_solar of C/O, could power a wide range of explosions/eruptions. Besides massive stars close to the Eddington limit and/or critical rotation, 8 -12 M_solar red supergiants, which are amongst the least bound of all stars, represent attractive candidates for transient phenomena.