Supermassive Stars as Gamma-Ray Bursters
Abstract
We propose that the gravitational collapse of supermassive stars (with masses greater than fifty thousand solar masses) could be a comological source of $\gamma$-ray bursts. A supermassive star would be de-stabilized as a result of the Feynman-Chandrasekhar instability and likely would collapse to a black hole, possibly releasing a fair fraction of its gravitational binding energy as thermal neutrino pairs. We show that neutrino/antineutrino annihilation- induced heating of the tenuous outer layers of such an object could drive electron/positron fireball formation, relativistic expansion, and associated $\gamma$-ray emission. There are two major advantages of this model. (1) Supermassive star collapses are far more energetic than solar mass-scale catastrophic events such as neutron-star/neutron-star mergers; therefore, the conversion of gravitational energy to fireball kinetic energy in the supermassive star scenario need not be highly efficient, nor is it necessary to invoke directional beaming. Further, the cooling time of afterglows in the supermassive star collapse model is naturally long enough to accomodate observational constraints. (2) There is no need for galaxy hosts, since the formation/collapse of supermassive stars could be pregalactic. We explore other distinctive features of the supermassive star collapse model, including the possibility of the Rayleigh-Taylor instability leading to multiple jet-like $e^\pm$-fireballs and, hence, multiple shocks and a rich time structure in $\gamma$-ray emission.Keywords
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