Science Opportunities of Wet Extreme Mass-Ratio Inspirals

Lyu, Zhenwei; Pan, Zhen; Mao, Junjie; Jiang, Ning; Yang, Huan

Science Opportunities of Wet Extreme Mass-Ratio Inspirals

Dec 27, 2024

17 pages

e-Print:

2501.03252 [astro-ph.HE]

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Abstract: (arXiv)

Wet extreme mass-ratio inspirals (wet EMRIs), which arise from stellar-mass black holes (sBHs) inspiral into supermassive black holes (SMBHs) within the gas-rich environments of Active Galactic Nuclei (AGN), are primary sources of gravitational waves (GWs) for space-borne detectors like LISA, TianQin, and Taiji. Unlike "dry EMRIs", which form through gravitational scattering in nuclear star clusters, wet EMRIs are naturally accompanied by interactions with accretion disks, offering rich multi-messenger science opportunities. They are distinct in generating transient electromagnetic (EM) signals, such as quasi-periodic eruptions (QPEs), which serve as valuable probes of accretion disk physics and SMBH environments. Their GW signals provide an unprecedented precision of the order of

O(10^{-4}\sim 10^{-6})

in measuring SMBH mass and spin, enabling the calibration of traditional EM techniques and offering insights into jet formation models. Additionally, wet EMRIs serve as bright and dark sirens for cosmology, facilitating percent-level precision measurements of Hubble parameter through AGN host identification or statistical association. These systems hold immense potential for advancing our understanding of black hole dynamics, accretion physics, and cosmology.

Note:

17 pages, 5 figures, 3 tables

References(2)

Figures(0)

[1]

Population III seeded Model [40-42] dN• d log M• = 0.01 M• 3 × 106M⊙ !-0.3 Mpc-3

[2]

Phenomenological Model [43] dN• d log M• = 0.002 M• 3 × 106M⊙ !+0.3 Mpc-3. In both cases, dN•/d log M• represents the number density of SMBHs per logarithmic mass interval. These mass functions were used in our previous studies [21, 23] to estimate the abundance of SMBHs in the range 104 ∼ 107 M⊙, which is particularly relevant for the formation and detection of EMRI. Our results demonstrated that wet EMRI could significantly enhance total and detectable EMRI rates, often dominating over dry EMRI. Recent studies based on optical observations of TDEs have provided an updated local SMBH mass function, which is nearly flat in logarithmic space [44], given by dN• d log M• = 0.005