Gravitational-Wave Radiation from Magnetized Accretion Disks

AbstractThe detectability of gravitational wave (GW) radiation from accretion disks is discussed based onvarious astrophysical contexts. In order to emit GW radiation, the disk shape should lose axial symmetry.We point out that a significant deformation is plausible in non-radiative hot accretion disks because ofenhanced magnetic activity, whereas it is unlikely for standard-type cool disks. We have analyzed the 3Dmagnetohydrodynamical (MHD) simulation data of magnetized accretion flow, finding non-axisymmetricdensity patterns. The corresponding ellipticity is ǫ ∼ 0.01. The expected time variations of GW radiationare overall chaotic, but there is a hint of quasi-periodicity. GW radiation has no interesting consequence,however, in the case of close binaries, because of very tiny disk masses. GW radiation is not significant,either, for AGN because of very slow rotation velocities. The most promising case can be found in gamma-ray bursts or supernovae, in which a massive torus (or disk) with a solar mass or so may be formed arounda stellar-mass compact object as the result of a merger of compact objects, or by the fallback of explodedmaterial towards the center in a supernova. Although much more intense GW radiation is expected beforethe formation of the torus, the detection of GW radiation in the subsequent accretion phase is of greatimportance, since it will provide a good probe to investigating their central engines.Key words: accretion, accretion disks — black holes — galaxies: Seyfert — gamma-ray bursts —gravitational wave