In article ,
jacob navia wrote:
Question then:

What is the maximal black hole accretion rate?

Answer: it depends.

For example, suppose I collect a bunch of stars, extract all their
angular momentum, and drop them one by one on radial trajectories into
a non-rotating black hole which already has a mass large enough that
the event horizon is the typical stellar radius. The accretion rate
is very high (limited only by how fast I can shove the stars in
without them colliding), the radiation generated is zero -- all the
kinetic energy generated as the star falls in is carried in with it
over the event horizon (advected). Obviously nobody is out there doing
this, but it illustrates that you have to understand what sort of
material is accreting and in what way before you can answer questions
about black hole growth rate.

Standard calculations such as the Eddington limit implicitly assume
radiatively efficient flows with an efficiency ~ 10%. They also assume
quasi-spherical symmetry. It is certainly possible (& observed) for
systems to exceed the Eddington 'limit'.

If you go to ADS and search abstracts for 'black hole growth early
universe' or something along those lines you will find a bunch of
people discussing different scenarios for black hole growth, including
some where the black holes do indeed grow rapidly without producing
much radiation in the early universe. Everybody working in this area
is aware (and has been for some time given the existence of high-z
quasars) that this needs to be understood.

Martin
--
Martin Hardcastle
School of Physics, Astronomy and Mathematics, University of Hertfordshire, UK
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