PPN--spin degeneracies in mock S62-like stellar-orbit inference
Abstract
We investigate the degeneracies between black hole (BH) spin effects and parametrized post-Newtonian (PPN) parameters in the relativistic orbital dynamics of S2-like and S62-like stars orbiting Sagittarius A∗. Using a 1PN+SO Hamiltonian framework and synthetic astrometric and radial velocity datasets, we perform Bayesian parameter inference. For current baseline observational precisions, the dominant relativistic observable--the Schwarzschild periapsis advance--allows the recovery of the effective precession parameter Υ, while leaving the individual PPN parameters γ and β degenerate. Assuming microarcsecond-level astrometric precision, the spin-induced Lense-Thirring signal becomes partially detectable; fixing the PPN sector to General Relativity allows the BH spin magnitude to be constrained to an uncertainty of ∼10−2. However, simultaneously varying PPN and spin parameters reveals a strong, approximately linear covariance between Υ and the dimensionless spin parameter χ. To overcome this limitation, we demonstrate that joint multi-star inference can disentangle the degeneracy by combining a wider-orbit star, which constrains the dominant 1PN sector, with a compact relativistic orbit that is sensitive to Lense-Thirring frame dragging.
Versions
Related
- Revisiting the Photometric Modulation Amplitudes of Kepler Planet Hosts: A Confounder-Adjusted Test of Stellar Spin-Orbit Alignment
- Stellar companions sculpt hot Jupiter formation and spin-orbit evolution
- Mock CSST NUV-NIR imaging of TNG50 galaxies with resolved stellar populations
- Binary-black hole spin population results may be driven by prior degeneracies
- The stellar orbit distribution of 24 late-type galaxies observed by MUSE
BibTeX
@misc{khlghatyan2026ppnspin,
title = {{PPN--spin degeneracies in mock S62-like stellar-orbit inference}},
author = {Shant Khlghatyan},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.05172},
eprint = {2609.05172},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.05172},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - PPN--spin degeneracies in mock S62-like stellar-orbit inference
AU - Shant Khlghatyan
PY - 2026
DA - 2026/09/04
PB - arXiv
DO - 10.48550/arxiv.2609.05172
UR - https://arxiv.org/abs/2609.05172
AB - We investigate the degeneracies between black hole (BH) spin effects and parametrized post-Newtonian (PPN) parameters in the relativistic orbital dynamics of S2-like and S62-like stars orbiting Sagittarius A^∗. Using a 1PN+SO Hamiltonian framework and synthetic astrometric and radial velocity datasets, we perform Bayesian parameter inference. For current baseline observational precisions, the dominant relativistic observable--the Schwarzschild periapsis advance--allows the recovery of the effective precession parameter Υ, while leaving the individual PPN parameters γ and β degenerate. Assuming microarcsecond-level astrometric precision, the spin-induced Lense-Thirring signal becomes partially detectable; fixing the PPN sector to General Relativity allows the BH spin magnitude to be constrained to an uncertainty of ∼10^−2. However, simultaneously varying PPN and spin parameters reveals a strong, approximately linear covariance between Υ and the dimensionless spin parameter χ. To overcome this limitation, we demonstrate that joint multi-star inference can disentangle the degeneracy by combining a wider-orbit star, which constrains the dominant 1PN sector, with a compact relativistic orbit that is sensitive to Lense-Thirring frame dragging.
ER -