Very extreme mass-ratio bursts in the Galaxy and neighbouring galaxies in relation to space-borne detectors (2004.04016v2)

Abstract: Two papers\citep{xmri1, xmri2} revealed that in our Galaxy there are very extreme-mass-ratio inspirals composed by brown dwarfs and the supermassive black hole at the center of the Galaxy. The event rates estimated in these papers are very considerable for future space-borne detectors. In addition, there are plunge events during the formation of inspiraling orbits. In this work, we calculate the gravitational waves from compact objects (brown dwarf, primordial black hole and etc.) plunging into or being scattered by the central supermassive black hole. We find that for space-borne detectors the signal-to-noise ratios of these bursts are quite high. The event rates are estimated as $\sim$ $0.01 {\rm{yr}^{-1}}$ for the Galaxy. If we are lucky, this kind of very extreme-mass-ratio bursts will offer a unique chance to reveal the nearest supermassive black hole and nuclei dynamics. The event rate can be as large as 4 $\sim$ 8 ${\rm yr^{-1}}$ in 10 Mpc, and because the signal is strong enough for observations by space-borne detectors, we have a good chance of being able to probe the nature of neighboring black holes.