Motivation and challenge to capture both large-scale and local transport in next generation accretion theory
Publikation: Bidrag til tidsskrift › Tidsskriftartikel › Forskning › fagfællebedømt
Dokumenter
- pdf
3,18 MB, PDF-dokument
> Accretion disc theory is less developed than stellar evolution
theory although a similarly mature phenomenological picture is
ultimately desired. While the interplay of theory and numerical
simulations has amplified community awareness of the role of magnetic
fields in angular momentum transport, there remains a long term
challenge to incorporate the insights gained from simulations into
improving practical models for comparison with observations. What has
been learned from simulations that can lead to improvements beyond SS73
in practical models? Here, we emphasize the need to incorporate the role
of non-local transport more precisely. To show where large-scale
transport would fit into the theoretical framework and how it is
currently missing, we review why the wonderfully practical approach of
Shakura & Sunyaev (Astron. Astrophys., vol. 24, 1973, pp. 337-355,
SS73) is necessarily a mean field theory, and one which does not include
large-scale transport. Observations of coronae and jets, combined with
the interpretation of results from shearing box simulations, of the
magnetorotational instability (MRI) suggest that a significant fraction
of disc transport is indeed non-local. We show that the Maxwell stresses
in saturation are dominated by large-scale contributions and that the
physics of MRI transport is not fully captured by a viscosity. We also
clarify the standard physical interpretation of the MRI as it applies to
shearing boxes. Computational limitations have so far focused most
attention toward local simulations, but the next generation of global
simulations should help to inform improved mean field theories. Mean
field accretion theory and mean field dynamo theory should in fact be
unified into a single theory that predicts the time evolution of spectra
and luminosity from separate disc, corona and outflow contributions.
Finally, we note that any mean field theory, including that of SS73, has
a finite predictive precision that needs to be quantified when comparing
the predictions to observations.
Originalsprog | Engelsk |
---|---|
Tidsskrift | Journal of Plasma Physics |
Vol/bind | 81 |
Udgave nummer | 5 |
Sider (fra-til) | 395810505 |
ISSN | 0022-3778 |
DOI | |
Status | Udgivet - 1 okt. 2015 |
Eksternt udgivet | Ja |
Antal downloads er baseret på statistik fra Google Scholar og www.ku.dk
Ingen data tilgængelig
ID: 166633197