Stability analysis of supermassive primordial stars: a new mass range for general relativistic instability supernovae

Observed supermassive black holes in the early Universe have several proposed formation channels in part because most of these channels are difficult to probe. One of the more promising channels, the direct collapse of a supermassive star has several possible probes including the explosion of a helium-core supermassive star triggered by a general relativistic instability. We develop a straightforward method for evaluating the general relativistic radial instability without simplifying assumptions and apply it to population III supermassive stars taken from a post Newtonian stellar evolution code. This method is more accurate than previous determinations and it finds that the instability occurs earlier in the evolutionary life of the star. Using the results of the stability analysis, we perform 1D general relativistic hydrodynamical simulations, and we find two general relativistic instability supernovae fuelled by alpha capture reactions as well as several lower mass pulsations, analogous to the puslational pair instability process. The mass range for the events (2.6-3.0 x10(4)M(circle dot)) is lower than that had been suggested by previous works (5.5 x10(4)M(circle dot)), because the instability occurs earlier in the star's evolution. The explosion may be visible to among others JWST, while the discovery of the pulsations opens up additional possibilities for observation.