The following is from Nature Contents this morning. Shame I can't get the full article...
Al.
Astrophysics: Magnetic accretion p938
Disks of hot gas drawn onto a central star or black hole are the best energy-producing machines in the Universe. So how do these accretion disks work? The answer, it seems, is blowing in their winds.
Daniel Proga
Editor's Summary
22 June 2006
The attraction of 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.
Letter
Nature 441, 953-955 (22 June 2006) | doi:10.1038/nature04912; Received 22 December 2005; Accepted 10 May 2006
The magnetic nature of disk accretion onto black holes
Jon M. Miller
1, John Raymond
2, Andy Fabian
3, Danny Steeghs
2, Jeroen Homan
4, Chris Reynolds
5, Michiel van der Klis
6 and Rudy Wijnands
6
Top of page Although disk accretion onto compact objects—white dwarfs, neutron stars and black holes—is central to much of high-energy astrophysics, the mechanisms that enable this process have remained observationally difficult to determine. Accretion disks must transfer angular momentum in order for matter to travel radially inward onto the compact object1. Internal viscosity from magnetic processes1, 2, 3, 4 and disk winds5 can both in principle transfer angular momentum, but hitherto we lacked evidence that either occurs. Here we report that an X-ray-absorbing wind discovered in an observation of the stellar-mass black hole binary GRO J1655 - 40 (ref. 6) must be powered by a magnetic process that can also drive accretion through the disk. Detailed spectral analysis and modelling of the wind shows that it can only be powered by pressure generated by magnetic viscosity internal to the disk or magnetocentrifugal forces. This result demonstrates that disk accretion onto black holes is a fundamentally magnetic process.
