Supermassive stars with random transverse magnetic fields

Abstract

\n 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 to be the progenitors or seeds of supermassive black holes that power quasars and active galactic nuclei. We study magnetostatic equilibria and magnetohydrodynamic (MHD) radial (in)stability properties of non-rotating SMSs with quasi-spherical symmetry involving random transverse magnetic fields (RTMFs) using general relativity (GR). With RTMFs, the maxima of the gravitational binding energy marks the GR MHD transition from stability to instability and the RTMF does not modify the GR stability criterion significantly when ${\\cal M}/\\left|\\Omega \\right|\\lesssim 0.1$ where $\\cal M$ is the total magnetic energy and Ω is the total gravitational potential energy. When $0.1\\lesssim {\\cal M}/\\left|\\Omega \\right|\\lesssim 1$, nevertheless, the critical 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\u2009M⊙ to ∼106\u2009M⊙ and higher. For ${\\cal M}/\\left|\\Omega \\right|\\sim 1$, the evolution track of SMS is shifted towards the redder part of the H-R diagram, suggesting 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 closely related to reports of LIGO-Virgo gravitational wave event scenario of binary BH mergers.