This is our (i.e., Caroline D’Angelo and I) new paper submitted for publication to The Astrophysical Journal and posted on the astro-ph archive (http://arxiv.org/abs/1304.6430; update: it’s now accepted: ApJ 771, 94).
We describe observational evidence for the existence of a new accretion disk solution called dead disk, which emerges under certain conditions when the magnetospheric radius is close to the co-rotation radius. We find evidence for a dead disk forming in one accreting millisecond X-ray pulsars (NGC 6440 X-2 and SAX J1808.4-3658, see also ApJ 707, 1296 for this latter source).
The disk-magnetosphere interaction has been studied for decades and still we do not know how large this region is and how the field and the disk interact in the inner regions when the accretion disk is disrupted and the accretion flow becomes magnetically channelled. With this new paper we provide a first direct constraint on the width of this region. There are also important consequences for the spin up/spin down of the neutron star as the dead disk solution is a different and alternative scenario to the famous propeller stage.