A Detection of Sgr A* in the Far Infrared

We report the first detection of the Galactic Centre massive black hole, Sgr A*, at 100 and 160 μm. Our measurements were obtained with PACS on board the Herschel satellite at 100 μ m and 160 μm. We measure a significant and simultaneous variation of its flux of Δ F_ν=160μm =(0.27±0.06) Jy and Δ F_{ν=100 μm} =(0.16±0.10) Jy during one observation. The significance level of the 160 μ m band variability is 4.5σ and the corresponding 100 μm band variability is significant at 1.6σ. We find no example of an equally significant false positive detection. Conservatively assuming a variability of 25% in the FIR, we can provide upper limits to the flux. The upper limits are consistent with modern ALMA and VLA observations. Our upper limits provide further evidence for a spectral peak at ∼ 10¹² Hz and constrain the number density of γ∼100 electrons in the accretion disk and or outflow.