On the “failure” of the Standard Model for Galactic Black Holes in Quiescence

It is currently believed that the “standard” accretion disk theory under-predicts the observed X-ray luminosity from Soft X-ray Transients (SXT) in quiescence by as much as 4 to 6 orders of magnitude. This “documented” failure of the standard model is considered to be one of the strongest arguments for the existence of the Advection Dominated Accretion Flows (ADAF) in Astrophysics, since these flows allow a much higher level of X-ray emission in quiescence, in agreement with the observations. Here we point out that, in stark contrast to the static standard disks, such disks in quiescence produce most of X-ray emission very far from the last stable orbit. Taking this into account, we demonstrate that these disks can accommodate the observed X-ray luminosities of SXTs rather naturally. We also suggest that the X-ray emission from the dwarf novae in quiescence may be dominated by that from the “accretion” belt of the white dwarf rather than the accretion disk or the boundary layer. Finally, we note that our theory predicts that Fe Kα lines from standard accretion disks in quiescence should be narrow even though the cold disk goes all the way down to the last stable orbit around a black hole. Subject headings: accretion, accretion disks —binaries:close —novae, cataclysmic variables — line: formation