The short-period S-stars S4711, S62, S4714 and the Lense-Thirring effect due to the spin of Sgr A$^\ast$

TL;DR

This paper derives analytical expressions for Lense-Thirring precessions of short-period S-stars orbiting Sgr A* considering arbitrary SMBH spin orientations, highlighting the challenges in measuring these effects due to current uncertainties.

Contribution

It provides explicit formulas for LT precessions of orbital elements of S-stars with arbitrary SMBH spin orientation, expanding beyond previous idealized assumptions.

Findings

LT precessions depend on SMBH spin orientation angles.

Systematic uncertainties dominate over LT signals with current data.

Analytical expressions enable better assessment of measurement prospects.

Abstract

Recently, some S-stars (S4711, S62, S4714) orbiting the supermassive black hole (SMBH) in Sgr A$^\ast$ with short orbital periods ($7.6\,\mathrm{yr}\leq P_\mathrm{b}\leq 12\,\mathrm{yr}$) were discovered. It was suggested that they may be used to measure the general relativistic Lense-Thirring (LT) precessions of their longitudes of ascending node $\mathit{\Omega}$ induced by the SMBH's angular momentum $\boldsymbol{J}_\bullet$. In fact, the proposed numerical estimates hold only in the particular case of a perfect alignment of $\boldsymbol{J}_\bullet$ with the line of sight, which does not seem to be the case. Moreover, also the inclination $I$ and the argument of perinigricon $\omega$ undergo LT precessions for an arbitrary orientation of $\boldsymbol{J}_\bullet$ in space. We explicitly show the analytical expressions of $\dot I^\mathrm{LT},\,\dot{\mathit{\Omega}}^\mathrm{LT},\,\omega^\mathrm{LT}$ in terms of the SMBH's spin polar angles $i^\bullet,\,\varepsilon^\bullet$ by finding the range of values for each of them in arcseconds per year ($^{\prime\prime}\,\mathrm{yr}^{-1}$). For each star, the corresponding values of $i^\bullet_\mathrm{max},\,\varepsilon^\bullet_\mathrm{max}$ and $i^\bullet_\mathrm{min},\,\varepsilon^\bullet_\mathrm{min}$ are determined as well, along with those $i_0^\bullet,\,\varepsilon_0^\bullet$ that cancel the LT precessions. The LT perinigricon precessions $\dot\omega^\mathrm{LT}$ are overwhelmed by the systematic uncertainties in the Schwarzschild ones due to the current errors in the stars' orbital parameters and the mass of Sgr A$^\ast$ itself. [Abridged]