A New Window for Testing the PPN in the Strong-Field Regime: Stellar Rotation of S301
Abstract
The recently discovered S301 star, with an orbital period of 8.7 years and eccentricity e = 0.982, reaches a pericenter of just 140 Rs --- approximately nine times closer than S2's ∼ 1200Rs --- offering an unprecedented laboratory for testing strong-field gravity. We demonstrate that S301's stellar spin precession provides a novel probe of the PPN parameter γ, scaling as (2γPPN + 1)/3 relative to general relativity (GR). For maximum projected velocity shifts of 46.1 km s−1, next-generation spectrographs could constrain γPPN to ∼ 10% precision. When combined with S301's orbital precession --- a substantial ∼ 1.95∘ pericenter advance per orbit (GR prediction), approximately an order of magnitude larger than S2's ∼ 0.2∘, constraining (2βPPN + 2γPPN − 1)/3 --- the spin measurement breaks the β-γ degeneracy. A MCMC analysis of projected S2 and S301 observations yields σβ≈ 2.3 × 10−4, with the γ precision limited by the spin precession measurement to σγ≈ 0.1. While the spin precession provides an independent consistency check, its true significance lies in probing gravity at ϕ/c2 ∼ 10−4 and v/c ∼ 0.08 --- four orders of magnitude stronger than Solar System tests and an order of magnitude stronger than current S-star constraints. This complementary approach opens a new window for testing the PPN framework in the strong-field regime and demonstrates the power of combining multiple stellar probes at the Galactic Center.
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BibTeX
@misc{khodadi2026window,
title = {{A New Window for Testing the PPN in the Strong-Field Regime: Stellar Rotation of S301}},
author = {Mohsen Khodadi and Salvatore Capozziello},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.06977},
eprint = {2609.06977},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.06977},
}
RIS
TY - UNPB
TI - A New Window for Testing the PPN in the Strong-Field Regime: Stellar Rotation of S301
AU - Mohsen Khodadi
AU - Salvatore Capozziello
PY - 2026
DA - 2026/09/07
PB - arXiv
DO - 10.48550/arxiv.2609.06977
UR - https://arxiv.org/abs/2609.06977
AB - The recently discovered S301 star, with an orbital period of 8.7 years and eccentricity e = 0.982, reaches a pericenter of just 140 R_s --- approximately nine times closer than S2's ∼ 1200R_s --- offering an unprecedented laboratory for testing strong-field gravity. We demonstrate that S301's stellar spin precession provides a novel probe of the PPN parameter γ, scaling as (2γ_PPN + 1)/3 relative to general relativity (GR). For maximum projected velocity shifts of 46.1 km s^−1, next-generation spectrographs could constrain γ_PPN to ∼ 10% precision. When combined with S301's orbital precession --- a substantial ∼ 1.95^∘ pericenter advance per orbit (GR prediction), approximately an order of magnitude larger than S2's ∼ 0.2^∘, constraining (2β_PPN + 2γ_PPN − 1)/3 --- the spin measurement breaks the β-γ degeneracy. A MCMC analysis of projected S2 and S301 observations yields σ_β≈ 2.3 × 10^−4, with the γ precision limited by the spin precession measurement to σ_γ≈ 0.1. While the spin precession provides an independent consistency check, its true significance lies in probing gravity at ϕ/c^2 ∼ 10^−4 and v/c ∼ 0.08 --- four orders of magnitude stronger than Solar System tests and an order of magnitude stronger than current S-star constraints. This complementary approach opens a new window for testing the PPN framework in the strong-field regime and demonstrates the power of combining multiple stellar probes at the Galactic Center.
ER -