Alternative possibility of GW190521: Gravitational waves from high-mass black hole-disk systems
Masaru Shibata, Kenta Kiuchi, Sho Fujibayashi, Yuichiro Sekiguchi
Abstract
We evolve high-mass disks of mass $15--50\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ orbiting a $50\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ spinning black hole in the framework of numerical relativity. Such high-mass systems could be an outcome during the collapse of rapidly rotating very massive stars. The massive disks are dynamically unstable to the so-called one-armed spiral-shape deformation with the maximum fractional density perturbation of $\ensuremath{\delta}\ensuremath{\rho}/\ensuremath{\rho}\ensuremath{\gtrsim}0.1$, and hence, high-amplitude gravitational waves are emitted. The waveforms are characterized by an initial high-amplitude burst with the frequency of $\ensuremath{\sim}40--50\text{ }\text{ }\mathrm{Hz}$ and the maximum amplitude of $(1--10)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}22}$ at the hypothetical distance of 100 Mpc and by a subsequent low-amplitude quasiperiodic oscillation. We illustrate that the waveforms in our models with a wide range of the disk mass resemble that of GW190521. We also point out that gravitational waves from rapidly rotating very massive stars can be the source for 3rd-generation gravitational-wave detectors for exploring the formation process of rapidly spinning high-mass black holes of mass $\ensuremath{\sim}50--100\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ in an early universe.