Because of their low efficiency, ADAFs are much less luminous than the Shakura–Sunyaev thin disks.
The solutions tend to be hot (close to the virial temperature), optically thin, and quasi-spherical (see
Figure 12). Their spectra are non-thermal, appearing as a power-law, often with a strong Compton
component. This makes them a good candidate for the Hard state observed in X-ray binaries (discussed in
Section 12.3).
ADAFs were formally introduced in the Newtonian limit through a series of papers by Narayan and
Yi [223, 224, 225
], followed closely by Abramowicz [6
, 7] and others [106], although the existence of this
solution had been hinted at much earlier [134, 257]. In the same spirit as we gave the equations for the
Novikov–Thorne solution in Section 5.3 for thin disks, we report the self-similar ADAF solution found by
Narayan and Yi [224]. Again we present the solution with the following scaling:
,
and
.
The rapid advection in ADAFs generally has two effects: 1) dissipated orbital energy can not be radiated
locally before it is carried inward and 2) the rotation profile is generally no longer Keplerian, although
Abramowicz [6] found solutions where the dominant cooling mechanism was advection, even when the
angular momentum profile was Keplerian. Fully relativistic solutions of ADAFs have also been found
numerically [13, 41]. Further discussion of ADAFs is given in the review article by Narayan and
McClintock [219].
http://www.livingreviews.org/lrr-2013-1 |
Living Rev. Relativity 16, (2013), 1
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