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A dark jet dominates the power output of the stellar black hole Cygnus X-1


Black holes undergoing accretion are thought to emit the bulk of their power in the X-ray band by releasing the gravitational potential energy of the infalling matter1. At the same time, they are capable of producing highly collimated jets of energy and particles flowing out of the system with relativistic velocities2. Here we show that the 10-solar-mass (10M) black hole in the X-ray binary Cygnus X-1 (refs 3–5) is surrounded by a large-scale (5 pc in diameter) ring-like structure that appears to be inflated by the inner radio jet6. We estimate that in order to sustain the observed emission of the ring, the jet of Cygnus X-1 has to carry a kinetic power that can be as high as the bolometric X-ray luminosity of the binary system. This result may imply that low-luminosity stellar-mass black holes as a whole dissipate the bulk of the liberated accretion power in the form of ‘dark’, radiatively inefficient relativistic outflows, rather than locally in the X-ray-emitting inflow.

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Figure 1: A jet-blown ring around the Galactic stellar black hole in Cygnus X-1.
Figure 2: The ring of Cygnus X-1: sketch of the model.
Figure 3: Optical counterpart of the radio ring of Cygnus X-1.


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We thank D. Mislis and R. Corradi for the Hα observation presented in this work. The Westerbork Synthesis Radio Telescope is operated by ASTRON (the Netherlands Foundation for Research in Astronomy) with support from the Netherlands Foundation for Scientific Research (NWO).

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Correspondence to Elena Gallo.

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Gallo, E., Fender, R., Kaiser, C. et al. A dark jet dominates the power output of the stellar black hole Cygnus X-1. Nature 436, 819–821 (2005).

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