Updated predictions for gravitational wave emission from TDEs for next generation observatories

TL;DR

This study refines gravitational-wave predictions for tidal disruption events (TDEs) by incorporating all GW harmonics in the energy spectrum and extending the population to repeated partial TDEs (rpTDEs). Using a semi-analytical framework with a harmonic energy spectrum $\frac{dE}{df}$ and a galaxy BH mass function, the authors compute per-event strains, SNRs, and the stochastic background for LISA and a deci-Hertz (dHz) mission, across full and repeated disruptions. Their main findings are that LISA is unlikely to detect fTDEs, whereas dHz observatories could detect main-sequence and white-dwarf fTDEs, with WD-fTDEs in dwarf galaxies offering the most promising detectable background (SNR ≈ 19 over 10 years). rpTDEs, though explored, yield negligible detection prospects, highlighting the crucial role of GW harmonics and population modeling for future deci-Hz GW astronomy and for probing intermediate-mass black holes in dwarfs and globular clusters.

Abstract

In this paper, we investigate the gravitational wave (GW) emission from stars tidally disrupted by black holes (TDEs), using a semi-analytical approach. Contrary to previous works where this signal is modeled as a monochromatic burst, we here take into account all its harmonic components. On top of this, we also extend the analysis to a population of repeated-partial TDEs, where the star undergoes multiple passages around the black hole before complete disruption. For both populations, we estimate the rate of individual GW-detections considering future observatories like LISA and a potential deci-Hertz (dHz) mission, and derive the GW background from these sources. Our conclusions, even if more conservative, are consistent with previous results presented in literature. In fact, full disruptions of stars will not be seen by LISA but will be important targets for dHz observatories. In contrast, GWs from repeated disruptions will not be detectable in the near future.

Figures (12)

• Figure 1: GW signal from a fTDE of a 0.1M$_\odot$ MS star disrupted by a $4\times 10^6\text{M}_{\odot}$ BH (grey lines) and GW signal from a fTDE of a WD of $0.5\text{M}_{\odot}$ disrupted by a $10^3\text{M}_{\odot}$ BH (red lines). We consider two possible source distances: 8 kpc (dashed lines) and 1 Mpc (dash-dot lines). In blue and orange we plot the noise amplitudes of LISA and DO, respectively.
• Figure 2: Detection rates of MS-fTDEs plotted for different SNR thresholds. The blue curve is calculated considering LISA as the detector, while the orange curve is obtained considering DO. The observation time for both instruments is assumed to be 10 years. The dashed black line is one event over 10 years.
• Figure 3: MS-fTDEs background (magenta curve) plotted with respect to the sensitivity curves of LISA (blue line), DO (orange line) and $\mu$Ares (black line).
• Figure 4: Detection rates of WD-fTDEs from dwarf galaxies (left panel) and from globular clusters (right panel) plotted for different SNR thresholds. The blue curve is calculated considering LISA as the detector, while the orange curve is obtained considering DO. The observation time for both instruments is assumed to be 10 years. The dashed black line is one event over 10 years. The occupation fraction is 1 for both scenarios.
• Figure 5: WD-fTDEs background from dwarf galaxies (dark green line, left panel) and WD-fTDEs background from globular clusters (light green line, right panel). We assume that the mass of the intermediate mass BH in each globular cluster is $10^3\text{M}_{\odot}$ and that the occupation fraction is equal to 1 for both scenarios. Both signals are plotted with respect to the sensitivity curves of LISA (blue line), DO (orange line) and $\mu$Ares (black line).