Pre-explosion dynamo in the cores of massive stars

Abstract

We propose a speculative scenario where dynamo amplification of magnetic fields in the core convective shells of massive stars, tens of years to hours before they explode, leads to envelope expansion and enhanced mass loss rate, resulting in pre-explosion outbursts (PEOs). The convective luminosity in the burning shells of carbon, neon, oxygen, and then silicon, are very high. Based on the behavior of active main sequence stars we speculate that the convective shells can trigger magnetic activity with a power of about 0.001 times the convective luminosity. Magnetic flux tubes might buoy outward, and deposit their energy in the outer parts of the envelope. This in turn might lead to the expansion of the envelope and to an enhanced mass loss rate. If a close binary companion is present, mass transfer might take place and lead to an energetic outburst. The magnetic activity requires minimum core rotation and that the stochastic magnetic activity be on its high phase. Only in rare cases these conditions are met, accounting for that only the minority of core collapse supernovae (CCSNe) experience PEO. Such a pre-explosion magnetic activity might have implications for the explosion mechanism itself.