Gravitational Collapse and Neutrino Emission of Population III Massive Stars

Pop III stars are the first stars in the universe. They do not contain metalsand their formation and evolution may be different from that of stars of latergenerations. In fact, according to the theory of star formation, Pop III starsmight have very massive components ($\sim 100 - 10000M_\odot$). In this paper,we compute the spherically symmetric gravitational collapse of these Pop IIImassive stars. We solve the general relativistic hydrodynamics and neutrinotransfer equations simultaneously, treating neutrino reactions in detail.Unlike supermassive stars ($\gtrsim 10^5 M_\odot$), the stars of concern inthis paper become opaque to neutrinos. The collapse is simulated until after anapparent horizon is formed. We confirm that the neutrino transfer plays acrucial role in the dynamics of gravitational collapse, and find also that the$\beta$-equilibration leads to a somewhat unfamiliar evolution of electronfraction. Contrary to the naive expectation, the neutrino spectrum does notbecome harder for more massive stars. This is mainly because the neutrinocooling is more efficient and the outer core is more massive as the stellarmass increases. Here the outer core is the outer part of the iron core fallingsupersonically. We also evaluate the flux of relic neutrino from Pop IIImassive stars. As expected, the detection of these neutrinos is difficult forthe currently operating detectors. However, if ever observed, the spectrum willenable us to obtain the information on the formation history of Pop III stars.We investigate 18 models covering the mass range of $300 - 10^4 M_\odot$,making this study the most detailed numerical exploration of sphericalgravitational collapse of Pop III massive stars. This will also serve as animportant foundation for multi-dimensional investigations.Comment: 32 pages, 11 figs, submitted to Ap