Supermassive Objects as Gamma-Ray Bursters
Abstract
We propose that the gravitational collapse of supermassive objects (${\rm M}\ga 5\times10^4\,{\rm M_\odot}$), either as relativistic star clusters or as single supermassive stars (which may still result from stellar mergers in dense star clusters), could be a cosmological source of $\gamma$-ray bursts. Collapsing supermassive objects could release a fraction of their huge gravitational binding energy as thermal neutrino pairs. (These events could provide the seeds of the supermassive black holes observed at the center of many galaxies.) We show that the accompanying neutrino/antineutrino annihilation-induced heating could drive electron/positron \lq\lq fireball\rq\rq\ formation, relativistic expansion, and associated $\gamma$-ray emission. There are two major advantages of this model. (1) Supermassive object 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 object scenario need not be highly efficient, nor is it necessary to invoke directional beaming. (2) There is no need for actively star-forming galaxy hosts, since the formation/collapse of supermassive objects may not be tied to the formation of ordinary stars.Keywords
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