2024MNRAS.527..428D

Six archival Chandra observations are matched with eight sets of radio data and studied in the context of the outflow method to measure and study the spin properties of $\rm {Sgr ~A^{*}}$. Three radio and X-ray data sets obtained simultaneously, or partially simultaneously, are identified as preferred for the purpose of measuring the spin properties of $\rm {Sgr ~A^{*}}$. Similar results are obtained with other data sets. Results obtained with the preferred data sets are combined and indicate weighted mean values of the spin function of $F = 0.62 \pm 0.10$ and dimensionless spin angular momentum of $a_* = 0.90 \pm 0.06$. The spin function translates into measurements of the black hole rotational mass, M_rot, irreducible mass, M_irr, and spin mass-energy available for extraction, M_spin, relative to the total black hole dynamical mass, M_dyn. Weighted mean values of (M_rot/M_dyn) = (0.53 ± 0.06), (M_irr/M_dyn) = (0.85 ± 0.04), (M_spin/M_dyn) = (0.15 ± 0.04), M_rot = (2.2 ± 0.3) × 10⁶ M_⊙, M_irr = (3.5 ± 0.2) × 10⁶ M_⊙, and M_spin = (6.2 ± 1.6) × 10⁵ M_⊙ are obtained; of course (M_rot/M_irr) = (0.62 ± 0.10) since (M_rot/M_irr) = F. Values obtained for $\rm {Sgr ~A^{*}}$ are compared with those obtained for M87 based on the published spin function, which indicate that M87 carries substantially more rotational energy and spin mass-energy relative to the total (i.e. dynamical) black hole mass, the irreducible black hole mass, and in absolute terms.