Can LISA See Inside the Little Red Dots?
Abstract
The Little Red Dots (LRDs) are compact, broad-line sources that appear to contain accreting black holes (BHs) embedded in dense gas. Proposed models for their central environments (including quasi-stars, radiative BH envelopes and super-Eddington accretion discs) predict gas densities at the radii probed by an extreme-mass-ratio inspiral that differ by many orders of magnitude. We compute the inspiral of a $10−−30\Msun$ BH for a range of LRD interior models, including environmental effects from the gas, and test with a mismatch criterion whether the resulting waveforms can be distinguished from vacuum and from one another. Dense interiors (Bondi-like free-fall cavities and radiative envelopes) produce measurable deviations from vacuum in essentially every detectable event. Convective quasi-star interiors are measurable for MBH≲105Msun and z≲0.6, while a co-rotating disc leaves no measurable imprint. In favorable cases the models are also mutually distinguishable. None of the 14 JWST LRDs at z>3.9 would be detectable with a 10Msun companion, but 30 of 31 LRDs at z<0.9 would be if their black holes are ∼100 times less massive than their virial estimates, and in many of them the interior's imprint would be measurable. Across the LRD population to z=6, a 4-yr LISA mission would yield $0.08−−0.8$ detectable events for 105Msun hosts and 10Msun companions ($1.5−−15$ for 30Msun) if LRD nuclei host inspirals at the rate of ordinary galactic nuclei. In dense clusters, where captures are plunges, this falls to ≲10−4.
Related
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BibTeX
@misc{gomez2026lisa,
title = {{Can LISA See Inside the Little Red Dots?}},
author = {Samuel Gómez Gómez and Xisco Jimenez Forteza and Carlos Palenzuela and Rosalba Perna},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.08964},
eprint = {2610.08964},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.08964},
}
RIS
TY - UNPB
TI - Can LISA See Inside the Little Red Dots?
AU - Samuel Gómez Gómez
AU - Xisco Jimenez Forteza
AU - Carlos Palenzuela
AU - Rosalba Perna
PY - 2026
DA - 2026/10/06
PB - arXiv
DO - 10.48550/arxiv.2610.08964
UR - https://arxiv.org/abs/2610.08964
AB - The Little Red Dots (LRDs) are compact, broad-line sources that appear to contain accreting black holes (BHs) embedded in dense gas. Proposed models for their central environments (including quasi-stars, radiative BH envelopes and super-Eddington accretion discs) predict gas densities at the radii probed by an extreme-mass-ratio inspiral that differ by many orders of magnitude. We compute the inspiral of a $10−−30\Msun$ BH for a range of LRD interior models, including environmental effects from the gas, and test with a mismatch criterion whether the resulting waveforms can be distinguished from vacuum and from one another. Dense interiors (Bondi-like free-fall cavities and radiative envelopes) produce measurable deviations from vacuum in essentially every detectable event. Convective quasi-star interiors are measurable for MBH≲10^5Msun and z≲0.6, while a co-rotating disc leaves no measurable imprint. In favorable cases the models are also mutually distinguishable. None of the 14 JWST LRDs at z>3.9 would be detectable with a 10Msun companion, but 30 of 31 LRDs at z<0.9 would be if their black holes are ∼100 times less massive than their virial estimates, and in many of them the interior's imprint would be measurable. Across the LRD population to z=6, a 4-yr LISA mission would yield $0.08−−0.8$ detectable events for 10^5Msun hosts and 10Msun companions ($1.5−−15$ for 30Msun) if LRD nuclei host inspirals at the rate of ordinary galactic nuclei. In dense clusters, where captures are plunges, this falls to ≲10^−4.
ER -