In article ,
wrote:
Alternately, knowing radius and area, I could compute the value if
I knew the fluence near the core of the MW, "What is the fluence
of photon energy near the center of the MW, in Watts per square
meter?"

[[Mod. note -- I educated-guess that the photon flux will be many
orders of magnitude less than the E=mc^2 equivalent of the infalling
matter flux. But specific numbers would be welcome.
-- jt]]

OK, back of the envelope: the energy density in starlight in the MW is
~ 10^-13 J/m^3: this is the dominant photon field (the CMB is about
half this). So the fluence is Uc/4 ~ 10^-5 W/m^2. For a 4 x 10^6 solar
mass black hole, R_S = 10^10 m, so the energy being added is ~ 1 x
10^16 W, or the equivalent of the accretion of 0.1 kg/s, or, in SMBH
terms, peanuts. All numbers to order of magnitude only. Assuming
I've not screwed up somewhere, the main error in this calculation is
taking a typical starlight energy density in the MW to represent the
energy density in the Galactic centre, but that won't get this number
more than ~ 1 order of magnitude higher.

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