Clocks around Sgr A*

TL;DR

This paper explores how stars and pulsars orbiting the Galactic centre's black hole can serve as precise clocks to detect relativistic effects, especially around pericentre, using wavelet analysis to distinguish these effects from Newtonian perturbations.

Contribution

It introduces a unified model for orbiting clocks near Sgr A* and proposes wavelet decomposition as a method to isolate relativistic signals from Newtonian noise.

Findings

Relativistic effects peak near pericentre of highly eccentric orbits.

Wavelet analysis can help disentangle relativistic signals from Newtonian perturbations.

Relativity effects are most detectable within a two-year window around pericentre.

Abstract

The S stars near the Galactic centre and any pulsars that may be on similar orbits, can be modelled in a unified way as clocks orbiting a black hole, and hence are potential probes of relativistic effects, including black hole spin. The high eccentricities of many S stars mean that relativistic effects peak strongly around pericentre; for example, orbit precession is not a smooth effect but almost a kick at pericentre. We argue that concentration around pericentre will be an advantage when analysing redshift or pulse-arrival data to measure relativistic effects, because cumulative precession will be drowned out by Newtonian perturbations from other mass in the Galactic-centre region. Wavelet decomposition may be a way to disentangle relativistic effects from Newton perturbations. Assuming a plausible model for Newtonian perturbations on S2, relativity appears to be strongest in a two-year interval around pericentre, in wavelet modes of timescale approximately 6 months.