Supermassive stars with random transverse magnetic fields

Abstract

ABSTRACT Gravitational dynamic collapses of supermassive stars (SMSs) triggered at certain critical stages may give rise to black holes (BHs) in a broad mass range that populate the Universe including the early Universe. SMSs have been speculated as the progenitors or seeds of supermassive BHs that power quasars and active galactic nuclei. We study quasi-spherical magnetostatic equilibria and magnetohydrodynamic (MHD) radial pulsational (in)stability properties of non-rotating SMSs involving random transverse magnetic fields (RTMFs) using the general relativity (GR). With RTMFs, the maxima of the gravitational binding energy mark the GR MHD transition from stability to instability and the RTMF does not modify the GR stability criterion significantly when the ratio ${\cal M}/\left|\Omega \right|\lesssim0.1$, where $\cal M$ is the total magnetic energy and Ω is the total gravitational potential energy. When $0.1\lesssim{\cal M}/\left|\Omega \right|\lesssim1$, nevertheless, the critical GR magnetostatic equilibria on the verge of GR MHD collapses or explosions may change drastically, raising the upper mass limit at the onset of GR MHD instability from ∼105 to ∼106 M⊙ and even higher. For ${\cal M}/\left|\Omega \right|\sim 1$, the evolution track of magnetized SMS is shifted towards the redder part of the Hertzsprung–Russell diagram, featuring a sort of ‘magnetic reddening’ associated with the stellar ‘magnetized envelope inflation’. By estimates, the RTMF energy stored in an SMS can be as large as ∼1057 erg, enough to power gamma-ray bursts, fast radio bursts, or other forms of powerful electromagnetic wave bursts. It is possible for magnetized massive stars to dynamically form BHs in the mass range from several tens to thousands of solar masses without necessarily triggering the central electron-positron e± instability inside such stars – this fact is highly pertinent to the reports of LIGO-Virgo gravitational wave event scenario of binary BH mergers.