The magnetic nature of disk accretion onto black holes

We can't see black holes, they are black on a black background. But we can see where they are, thanks to the bright glow emitted by matter as it falls into the black hole. This disk accretion process is central to much of high-energy astrophysics, but observational clues as to its inner workings are rare. Using remarkable spectra obtained from the stellar-mass black-hole binary GRO J1655–40, Miller et al. have now achieved the long-sought goal of setting observational constraints on the nature of disk accretion onto compact objects. The spectra record an X-ray-absorbing wind that must be powered by a magnetic process that can also drive accretion through the disk. This demonstrates that disk accretion onto black holes is a fundamentally magnetic process.