Alternative possibility of GW190521: Gravitational waves from high-mass black hole-disk systems

Abstract

We evolve high-mass disks of mass 15–50 M⊙ orbiting a 50 M⊙ 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 δρ/ρ≳0.1, and hence, high-amplitude gravitational waves are emitted. The waveforms are characterized by an initial high-amplitude burst with the frequency of ∼40–50 Hz and the maximum amplitude of (1–10)×10⁻²² 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 ∼50–100 M⊙ in an early universe.