Gravitational Redshift Experiment with the Space Radio Telescope RadioAstron

TL;DR

This paper proposes a novel experiment using the RadioAstron space radio telescope to test gravitational redshift with unprecedented accuracy by leveraging its unique hardware and orbit, potentially improving current results tenfold.

Contribution

It introduces a new experimental setup utilizing RadioAstron's stable hydrogen maser and eccentric orbit to measure gravitational redshift more precisely than previous tests.

Findings

Estimated 30 hours of observation needed for 2×10⁻⁵ accuracy

Potential tenfold improvement over current gravitational redshift measurements

Utilizes RadioAstron's unique hardware and orbit for fundamental physics tests

Abstract

A unique test of general relativity is possible with the space radio telescope RadioAstron. The ultra-stable on-board hydrogen maser frequency standard and the highly eccentric orbit make RadioAstron an ideal instrument for probing the gravitational redshift effect. Large gravitational potential variation, occurring on the time scale of $\sim$24 hr, causes large variation of the on-board H-maser clock rate, which can be detected via comparison with frequency standards installed at various ground radio astronomical observatories. The experiment requires specific on-board hardware operating modes and support from ground radio telescopes capable of tracking the spacecraft continuously and equipped with 8.4 or 15 GHz receivers. Our preliminary estimates show that $\sim$30 hr of the space radio telescope's observational time are required to reach $\sim 2\times10^{-5}$ accuracy in the test, which would constitute a factor of 10 improvement over the currently achieved best result.