aIs 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?

--
Rich

[[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".

I don't know offhand what (if any) limits there are for M31 or maybe
other galaxies.
-- jt]]