On Tuesday, October 11, 2016 at 12:39:59 PM UTC-7, Steve Willner wrote:
In article 20161004070749.GA495@sirius,
Martin Hardcastle m.j.hardcastle writes:
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).

You could do a better job by looking up the stellar density near the
Galactic center and assuming a mass-to-light ratio. M/L will be
somewhere near 1 in solar units,

Thanks....
Best I found for stellar density is "several" hundred thousand stars per
cubic pc "very near" the center (so far anyway).

http://abyss.uoregon.edu/~js/ast122/lectures/lec26.html

using 0.1 pc for "very near" and 300,000 stars per pc^3 for "several
hundred thousand" as guesses, I get Energy Density = 1.22E-11 J/m^3

This is energy from stars L within sphere 0.1pc radius being emitted
outward (and in all directions) per second, divided by A at 0.1pc radius

This is about 100x Martin's previous envelope estimate, so pretty close,
and increases energy flow into MWBH to about 10kg/s equivalent mass flow
rate.

This is also 1.22E-11 Pa, which is close to values estimated for
cosmological dark energy.

Wiki gives two values, which when converted to energy yield 6E-10 and
9E-11, J/m^3 = Pa so the value I get (1.22E-11Pa) is about in between.

Sound about right?

Thanks for the help.

Ross