High-Frequency Gravitational Waves From Supermassive Black Holes: Prospects for Ligo-Virgo Detections

Abstract

It is commonly assumed that ground-based gravitational wave (GW) instruments will not be sensitive to supermassive black holes (SMBHs) because the characteristic GW frequencies are far below the ∼ 10 − 1000 Hz sensitivity bands of terrestrial detectors. Here, however, we explore the possibility of SMBH gravitational waves to leak to higher frequencies. In particular, if the high frequency spectral tail asymptotes toh( f ) ∝ f −α , where α ≤ 2, then the spectral amplitude is a constant or increasing function of the mass M at a fixed frequency f ≫ c 3 /GM. This will happen if the time domain waveform or its derivative exhibits a discontinuity. Ground based instruments could search for these universal spectral tails to detect or rule out such features irrespective of their origin. We identify the following processes which may generate high frequency signals: (i) gravitational bremsstrahlung of ultrarelativistic objects in the vicinity of a SMBH, (ii) ringdown modes excited by an external process that has a high frequency component or terminates abruptly, (iii) gravitational lensing echos and diffraction. We estimate the order of magnitude of the detection signal to noise ratio for each mechanism (i, ii, and iii) as a function of the waveform parameters. In particular for (iii), SMBHs produce GW echos of inspiraling stellar mass binaries in galactic nuclei with a delay of a few minutes to hours. The lensed primary signal and GW echo are both amplified if the binary is within a ∼ 10 deg(r/100M) −1/2 cone behind the SMBH relative to the line of sight at distance r from the SMBH. For the rest of the binaries near SMBHs, the amplitude of the GW echo is ∼ 0.1(r/100M) −1 of the primary signal on average.

Gravitational lensing effects on parameter estimation in gravitational wave detection with advanced detectors

“…1 we do see that for the whole frequency band of AdvLIGO there is a significant amplitude modulation which comes from lensing. This kind of modulation can be used to extract the information of the supermassive black hole, which has already been pointed out in [34]. We will analyze this extraction quantitatively in the next section.…”

Astrophysical Gravitational-Wave Echoes from Galactic Nuclei

“…4 Similar to EM waves, the amplitudes of the scattered GW signals decay asymptotically exponentially with the order of the scattered waves (e.g. Zenginoǧlu & Galley 2012;Kocsis 2013) indicating that the detections of secondary scattered GWs are typically the most prominent besides the primary GWs.…”

Repeated gravitational lensing of gravitational waves in hierarchical black hole triples

“…The lens itself has been imagined as an intervening mass at a large distance from the observer and from the source [e.g., Refs. [16][17][18], but also as a supermassive BH (SMBH) that an inspiraling BBH orbits in an hierarchical triple [19]. The latter case, most rele- * Electronic address: daniel.dorazio@cfa.harvard.edu vant to this study, considers observables in the magnified GW echoes caused by lensing-induced time delays; these calculations were carried out for a source that is stationary with respect to the SMBH lens.…”