The Spin Angular Momentum and Black Hole Mass Components of Sagittarius A*

Abstract

The dimensionless spin angular momentum, dimensionless spin function, and blackhole mass components of Sagittarius A* (Sgr A*) were obtained by Daly et al. (2024) by applying the outflow method to six independent sets of simultaneously or contemporaneously obtained X-ray and radio data. Here, results obtained for Sgr A* with the outflow method are reviewed. Consistent results were obtained with each data set. Set I (the preferred data set) indicates that Sgr A* has a dimensionless spin angular momentum $a_{\ast }=(0.90\pm 0.06)$ and a dimensionless spin function $F=(0.62\pm 0.10)$. The results are consistent with the value of $a_{\ast }=(0.93\pm 0.15)$ obtained with the outflow method applied to an independent data set (Daly 2019). The application of the outflow method to a weak compact radio source such as Sgr A* in its current state is most accurately determined with simultaneous or contemporaneous radio and X-ray measurements.

6 pages, summary of oral report presented at the Galactic Center workshop 2026 (IAU Symposium 405, Traversing the Galactic Center in Space and Time)