On the Tidal Capture of White Dwarfs by Intermediate-mass Black Holes in Dense Stellar Environments

TL;DR

This paper explores how white dwarfs can be captured and disrupted by intermediate-mass black holes in dense star clusters, providing potential observational signatures like gravitational waves and high-energy emissions to confirm their existence.

Contribution

It estimates capture rates and predicts multi-messenger signals, offering new methods to detect and confirm intermediate-mass black holes in stellar environments.

Findings

Capture rate of ~1 per million years in galactic nuclei

Detectable gravitational waves by LISA for IMBHs around 10^4 solar masses

Bright X-ray and gamma-ray emissions detectable by current and future telescopes

Abstract

Intermediate-mass black holes (IMBHs) are the missing link between stellar-mass and supermassive black holes, widely believed to reside in at least some dense star clusters, but not yet observed directly. Tidal disruptions of white dwarfs (WDs) are luminous only for black holes less massive than $\sim 10^5\,M_{\odot}$, therefore providing a unique smoking gun that could finally prove the existence of IMBHs beyond any reasonable doubt. Here, we investigate the tidal captures of WDs by IMBHs in dense star clusters, and estimate a typical rate of $\sim 1\,{\rm Myr}^{-1}$ for galactic nuclei and $\sim 0.01\,{\rm Myr}^{-1}$ for globular clusters. Following the capture, the WD inspirals onto the IMBH producing gravitational waves detectable out to $\sim100$ Mpc by LISA for $\sim 10^4\,M_{\odot}$ IMBHs. The subsequent tidal stripping/disruption of the WD can also release bright X-ray and gamma-ray emission with luminosities of at least $\gtrsim10^{40}\,\rm{erg\,s^{-1}}$, detectable by \textit{Chandra}, \textit{Swift}, and upcoming telescopes, such as the \textit{Einstein Probe}.