The European Space Agency was watching the jets:
Astronomers using ESA’s Herschel space observatory have detected emission from the base of black-hole jets for the first time. While studying the black-hole binary system GX 339-4 in a multi-wavelength observation campaign, they noticed changes in the source’s X-ray and radio emissions signalling the onset of powerful jets being released from the black hole’s vicinity. This prompted the astronomers to observe the source at far-infrared wavelengths with Herschel. As the first observation of emission from jets in a black-hole binary system at these wavelengths, the data have allowed the astronomers to probe the jets down to their base, where the far-infrared emission originates.