First Sagittarius A* Event Horizon Telescope Results. VII. Polarization of the Ring

Abstract

The Event Horizon Telescope observed the horizon-scale synchrotron emission region around the Galactic center supermassive black hole, Sagittarius A* (Sgr A*), in 2017. These observations revealed a bright, thick ring morphology with a diameter of 51.8 ± 2.3 μas and modest azimuthal brightness asymmetry, consistent with the expected appearance of a black hole with mass M ≈ 4 × 106 M ⊙. From these observations, we present the first resolved linear and circular polarimetric images of Sgr A*. The linear polarization images demonstrate that the emission ring is highly polarized, exhibiting a prominent spiral electric vector polarization angle pattern with a peak fractional polarization of ∼40% in the western portion of the ring. The circular polarization images feature a modestly (∼5%–10%) polarized dipole structure along the emission ring, with negative circular polarization in the western region and positive circular polarization in the eastern region, although our methods exhibit stronger disagreement than for linear polarization. We analyze the data using multiple independent imaging and modeling methods, each of which is validated using a standardized suite of synthetic data sets. While the detailed spatial distribution of the linear polarization along the ring remains uncertain owing to the intrinsic variability of the source, the spiraling polarization structure is robust to methodological choices. The degree and orientation of the linear polarization provide stringent constraints for the black hole and its surrounding magnetic fields, which we discuss in an accompanying publication.

Enhanced Blandford Znajek jet in loop quantum black hole

“…This phenomenon halts the accretion process temporarily. A strong and ordered magnetic field is observed in Sgr A * in the recent polarimetric observation results [64,65]. MAD is currently the most favored one.…”

“…Similarly, this limitation applies to Sgr A * if the BH spin is relatively low (a ≲ 0.1), as suggested by [78]. However, subsequent observations by the EHT suggest a relatively high spin for Sgr A * (a ≳ 0.5) [63][64][65]. The conclusion of high BH spin for M 87 * and Sgr A * is made under the assumption of Kerr spacetime.…”

“…MAD is currently the most favored one. However, even MAD can not pass all the observational JCAP05(2024)101 constraints (especially the variability constraint) made by EHT [64,65]. Thus, the accretion flow models of Sgr A * are still under debate [38,39,68,69].…”