In article , brad
writes:

jacobnavia
[[Mod. note -- I think the author meant to say the the following two
quoted lines were writtey by jacobnavia. -- jt]]
Couldn't a symmetrical population of dead and invisible halo stars make
for the modified gravity we see?

No. The CMB also illuminates the matter power spectrum of the Universe.
That spectrum incorporates anything that generates a gravitational field.
And that spectrum analysis compares favorably with B.B. Neucleosynthesis
predictions. In other words, it includes all black holes...So looking through
better telescopes for previously unseen objects won't reveal anything not
already accounted for.

As far as the CMB goes, one has constraints on the total density and the
baryonic density. The CMB can't say what either is composed of, what
mass range, etc. Stellar-mass black holes as dark matter (which would
have to be primordial and hence non-baryonic because of BBN constraints)
would be compatible with the CMB, but are ruled out because microlensing
surveys don't detect them.

The dark matter could be all in primordial black holes, as long as they
are not all of the same mass (which would be strange anyway), but these
would have to be much less and/or much more massive than stars.