Long-term evolution of a collapsar

During the collapse of a massive star greater than 35-40 M _⊙, stellar core is considered to promptly collapse to a black hole, and stellar material may fall onto the hole greater than several solar masses with extremely high accretion rates (> 1 M_⊙ s ^-1). If the star has a sufficiently high angular momentum before the collapse, an accretion disk is likely to form around the black hole. Jets are suggested to be launched from the inner region of the accretion disk near the hole through magnetic and/or neutrino processes. Gamma-Ray Bursts (GRBs) are expected to be driven by the jets. This scenario of GRBs is called the collapsar model. Recently, magnetohydrodynamic (MHD) simulations were performed of the collapse of rapidly rotating, magnetized 25 M_⊙ and 40 M _⊙ stars in light of the collapsar model of GRBs (see papers listed at the end of the paper). For assumed angular velocity distributions and the uniform magnetic fields, the collapsars are shown to eject jets driven through the magnetic pressure. The simulations are however performed up to 4 s, which are shorter than durations of long GRBs ∼ 10 s. In the present work, we have performed long-term (∼ 10 s), two-dimensional, MHD simulations of the collapse of a rapidly rotating, magnetized 40 M_⊙ star.