Milky Way's black hole is quiet now but was far more active in the recent past

XRISM resolved the iron Fe Kα emission from the molecular cloud G0.11-0.11 and identified X-ray fluorescence, which the authors report indicates past strong X-ray flares from Sagittarius A* a few hundred to around a thousand years ago.

Astronomers used the XRISM X-ray observatory to study a molecular cloud near the center of the Milky Way. XRISM resolved the Fe Kα emission line in the cloud G0.11-0.11 with much greater spectral detail than previous telescopes. That detailed measurement lets researchers distinguish between two possible emission mechanisms. The authors report the pattern of emission is consistent with X-ray fluorescence caused by past activity from Sagittarius A*. Key findings: - XRISM/Resolve resolved the Fe Kα doublet from the Galactic Center molecular cloud G0.11-0.11 for the first time. - The line profile is consistent with X-ray fluorescence rather than cosmic-ray ionization, the authors report. - The fluorescence signal implies Sagittarius A* produced strong X-ray outbursts a few hundred to about a thousand years ago, according to the paper. - Sagittarius A* is currently very dim and is described as inactive. Summary: The XRISM observations provide a new, higher-resolution way to read past activity at the Galactic center and to discriminate between emission models for molecular clouds. The results support scenarios in which one or more past X-ray flares from Sagittarius A* illuminated nearby clouds. Future X-ray monitoring of Galactic Center molecular clouds is expected to test one-flare versus two-flare models and to build a more detailed map of the region.