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arXiv · 2606.25549

Gravitational Light Deflection with SKA-VLBI and Its Application to Precision Tests of General Relativity

Y. J. Li·J. J. Li·Z. H. Lin·D. J. Liu·Y. W. Dong·C. J. Hao·Y. Xu
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Abstract

Experimental test of general relativity remains an ongoing endeavour. Radio astrometry provides a vital tool for precisely measuring the light deflection caused by the Sun, testing general relativity, and discriminating between gravitational theories. The best accuracy for the post-Newtonian relativistic parameter, $\gamma$, achieved with very long baseline interferometry is $9 \times 10^{-5}$. With 300-sec integration, SKA-VLBI can achieve a sensitivity of $\sim$15 $\mu$Jy at 15 GHz over a bandwidth of 0.256 GHz. This enables detection of $\sim$36 extragalactic radio sources per square degree with flux densities of $\sim$1.5 mJy, and potentially detecting in-beam radio sources. Single-epoch SKA-VLBI observations may achieve an astrometric precision of $\sim$2 $\mu$as. Utilising the Sun as a gravitational lens, 10-epoch positional tracking of extragalactic sources could improve $\gamma$ accuracy to $\sim$10$^{-7}$. Even with Jupiter as a lens, SKA-VLBI can measure $\gamma$ to $\sim$10$^{-4}$. Critically, it may conduct the first measurement of quadrupolar deflection of light caused by Jupiter, determining the physical oblateness of Jupiter, $J_{\mathrm{2, J}}$, to within $\sim${}$10^{-3}$. These advances are expected to rigorously test and improve gravitational theories or high-order parameterized post-Newtonian formalisms, while laying the foundations for (sub)$\mu$as astrometry.

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Y. J. Li, J. J. Li, Z. H. Lin, D. J. Liu, Y. W. Dong, C. J. Hao, Y. Xu. 2026-06-24. Gravitational Light Deflection with SKA-VLBI and Its Application to Precision Tests of General Relativity. https://arxiv.org/abs/2606.25549

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