Spherical collapse of supermassive stars: Neutrino emission and gamma-ray bursts

Abstract

Abstract. We present the results of numerical simulations of the spherically symmetric gravitational collapse of supermassive stars (SMS). The collapse is studied using a general relativistic hydrodynamics code. The coupled system of Einstein and fluid equations is solved employing coordinates adapted to a foliation of the spacetime by means of outgoing null hypersurfaces. The code contains an equation of state which includes effects due to radiation, electrons and baryons, and detailed microphysics to account for electron-positron pairs. In addition energy losses by thermal neutrino emission are included. We are able to follow the collapse of SMS from the onset of instability up to the point of black hole formation. Several SMS with masses in the range 5 × 10 5 M −10 9 M are simulated. In all models an apparent horizon forms initially, enclosing the innermost 25% of the stellar mass. From the computed neutrino luminosities, estimates of the energy deposition by νν-annihilation are obtained. Only a small fraction of this energy is deposited near the surface of the star, where, as proposed recently by , it could cause the ultrarelativistic flow believed to be responsible for γ-ray bursts. Our simulations show that for collapsing SMS with masses larger than 5 × 10 5 M the energy deposition is at least two orders of magnitude too small to explain the energetics of observed long-duration bursts at cosmological redshifts. In addition, in the absence of rotational effects the energy is deposited in a region containing most of the stellar mass. Therefore relativistic ejection of matter is impossible.

Numerical Study of Stellar Core Collapse and Neutrino Emission: Probing the Spherically Symmetric Black Hole Progenitors with 3–30M⊙Iron Cores

“…Similarly, numerical studies on black hole formation have also been produced recently (e.g., Fryer 1999;Linke et al 2001;Fryer et al 2001, hereafter FWH01;Sekiguchi & Shibata 2005, hereafter SS05;Nakazato et al 2006, hereafter NSY06;Sumiyoshi et al 2006, hereafter SYSC06). Fryer (1999) classified core collapse into three types: (a) Stars with M P 25 M make explosions and produce neutron stars.…”

“…FWH01 also computed the collapse of a rotating star with 300 M under Newtonian gravity and showed that it has a weak bounce and then recollapses to a black hole immediately. As for the collapse of supermassive stars with M k 5 ; 10 5 M , Linke et al (2001) found that they form black holes without bounce before becoming opaque to neutrinos.…”

The neutrino signal from protoneutron star accretion and black hole formation

“…The actual progenitor mass limits for these different scenarios are a subject of debate and depend on the explosion mechanism and the input physics. The fate of progenitors more massive than 75 M differs from the usual Fe-core collapse scenario by the appearance of the pairinstability, as studied by Fryer et al (2001), Linke et al (2001), , Nomoto et al (2005), Ohkubo et al (2006) and Nakazato et al (2007).…”

Collapse of a Rotating Supermassive Star to a Supermassive Black Hole: Fully Relativistic Simulations

“…To accelerate 570M the collapse, we depleted the pressure by 1% initially. During the evolution, we adopted a G-law equation of state according to , where denotes the specific internal energy P p (G Ϫ 1)re e of the fluid, thereby treating the gas as an ideal, adiabatic fluid in which cooling can be ignored on a dynamical timescale (Linke et al 2001).…”