On November 27, Phillip Helbig (undress to reply) wrote:
Is it possible that the missing mass, the 'dark matter',
consists of two generations of burned out stars?
These would be short lifetimes, hence large masses,
according to star formation theory, hence mostly black holes
or neutron stars. I don't see that as a problem.
What are the counter-arguments?

There are several.

[[Mod. note -- Microlensing studies show that at most a small fraction
of the dark matter in the Milky Way's halo can be in compact objects
of stellar mass. For example, the EROS project
https://arxiv.org/abs/astro-ph/0607207
concluded that "machos in the mass range 0.6e-7 M_sun M 15 M_sun
are ruled out as the primary occupants of the Milky Way Halo".

Right.
I was co-author on a paper which pointed out that a significant fraction
of dark matter can't be on compact objects between us and quasars (i.e.
in most of the observable universe), otherwise this would be seen in
quasar light curves (which, despite some claims to the contrary, is not
the case):

http://www.astro.multivax.de:8000/he...sing_qsos.html
http://adsabs.harvard.edu/abs/2003A&A...408...17Z

I'm unfamiliar with this technique - microlensing refers
to the occlusion of distant bright objects, by nearer objects?
Thus gravitational lensing effects?

I don't understand the primacy of the masses.
Wouldn't the statistics depend on the volume of
the 'dark' objects? That is, their solid angle arc,
how much of the sky they cover?

I don't find the reasoning compelling. You looked
at quasar variability, and concluded that MACHO
doesn't explain it. Isn't it a big leap to say such
objects don't exist at all?

Also, big-bang nucleosynthesis tells us what fraction of the universe
is in baryons; there is no way that stars, being baryonic, could make
up a significant fraction of dark matter.

Seeing that 80% of the mass of the mass is 'missing', of
unknown character, all such origin theories are suspect.

--
Rich