Tidal Disruption of Blanets by Supermassive Black Holes: From Test Particles to Planetary-Mass Bodies in Kerr Spacetime
Abstract
Planetary-mass bodies formed in active galactic nucleus (AGN) discs, termed "blanets", may undergo tidal disruption by the central supermassive black hole (SMBH). We analyse this process in Kerr spacetime using Mino-time geodesics and the Marck tidal tensor in a parallel-transported tetrad, treating the blanet as a test particle with finite size entering through the disruption criterion. For a blanet of 100 M⊕ and 6 R⊕ around a 107 M⊙ SMBH, the tidal radius is 0.82 AU, or 8.3 gravitational radii, requiring a non-perturbative relativistic treatment. The Hills mass depends on bulk density as MHills∝ρp−1/2 and is independent of blanet mass at fixed density. Rocky compositions yield a lower Hills mass than a Sun-like star, while volatile-rich compositions yield a higher value, suggesting a potential composition diagnostic. The frozen-in fallback model gives a peak time of about 15 yr and a peak luminosity of 3.7×1040 erg/s, about 3×10−5 of the Eddington luminosity, predicting a faint, ultraviolet-peaked transient lasting roughly a century. Scalar resonant relaxation in the surrounding nuclear star cluster may deliver blanets to disruptive orbits over 108 to 109 yr, implying an estimated per-AGN event rate of 10−7 to 10−6 per year. Gravitational waves from sub-Earth-mass debris fragments remain approximately nine orders of magnitude below Laser Interferometer Space Antenna sensitivity.
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BibTeX
@misc{pandey2026tidal,
title = {{Tidal Disruption of Blanets by Supermassive Black Holes: From Test Particles to Planetary-Mass Bodies in Kerr Spacetime}},
author = {Shreesham Pandey and Sunita Singh},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2606.06884},
eprint = {2606.06884},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.06884},
}
RIS
TY - UNPB
TI - Tidal Disruption of Blanets by Supermassive Black Holes: From Test Particles to Planetary-Mass Bodies in Kerr Spacetime
AU - Shreesham Pandey
AU - Sunita Singh
PY - 2026
DA - 2026/09/14
PB - arXiv
DO - 10.48550/arxiv.2606.06884
UR - https://arxiv.org/abs/2606.06884
AB - Planetary-mass bodies formed in active galactic nucleus (AGN) discs, termed "blanets", may undergo tidal disruption by the central supermassive black hole (SMBH). We analyse this process in Kerr spacetime using Mino-time geodesics and the Marck tidal tensor in a parallel-transported tetrad, treating the blanet as a test particle with finite size entering through the disruption criterion. For a blanet of 100 M_⊕ and 6 R_⊕ around a 10^7 M_⊙ SMBH, the tidal radius is 0.82 AU, or 8.3 gravitational radii, requiring a non-perturbative relativistic treatment. The Hills mass depends on bulk density as M_Hills∝ρ_p^−1/2 and is independent of blanet mass at fixed density. Rocky compositions yield a lower Hills mass than a Sun-like star, while volatile-rich compositions yield a higher value, suggesting a potential composition diagnostic. The frozen-in fallback model gives a peak time of about 15 yr and a peak luminosity of 3.7×10^40 erg/s, about 3×10^−5 of the Eddington luminosity, predicting a faint, ultraviolet-peaked transient lasting roughly a century. Scalar resonant relaxation in the surrounding nuclear star cluster may deliver blanets to disruptive orbits over 10^8 to 10^9 yr, implying an estimated per-AGN event rate of 10^−7 to 10^−6 per year. Gravitational waves from sub-Earth-mass debris fragments remain approximately nine orders of magnitude below Laser Interferometer Space Antenna sensitivity.
ER -