(alpha) Dark Matter - what is it?

i wonder if the oldest galaxies have all stars cold by now
No, not all the stars. Some of the smaller stars in them yes, but not most. White dwarfs (cores of red giants) take a long time to cool and if star was more than 1.4 solar masses, there is an even denser, smaller relic left behind, very slowly cooling.
This thread (sugggesting many "solar size" black holes exist) is sinking into the abysis, (OK with me, if no one interested), but as one last effort to revive it, I repost part of post 61 (the whole intended program is set forth in post 1):

The last iron forming stage of fusion requires enormous temperatures and still only the extreme “tail of the velocity distribution” can make collisions that lead to formation of iron. Thus, the rate of fusion formation of iron is very strongly dependant upon the local temperature and only depends quadratic on the density of the particles which will fuse to form the iron. At least crudely, if not exactly, the product of T, the local temperature, and D, the local density is proportional to the local pressure, P. Surely P(r), where r is the radial distance from the center of mass is a monotonically decreasing function of r, but that does not require that T always be. (To keep the explanation of the idea clear, I ignore that D = D1, +D2 + Di +… where even here only the three most important components for the fusion are explicit. Di is the density of the iron ions and perhaps the dominate “fuels“, D1 and D2, are the same ions. )

Because the temperature is so high, the magnitude of the relative small statistical temperature fluctuations are not negligible, especially in view of the strong dependency of the fusion rate upon temperature. I.e. some small region near, but not at the exact mass center of the star, is likely to be making iron more rapidly than at the exact mass center of the star. This slightly higher fusion rate, at r = a > 0, (only at some latitude and longitude, of course, but I avoid giving these coordinates.) initiates a self-accelerating thermal instability. I.e. any small volume, statistically hotter than average for that radius spot, will rapidly become much hotter and produce iron more rapidly despite the constantly falling D which keeps P(a) at that spot equal to P(a) at other colder spots, equally distant from the mass center. Note also that R >> a, were R is the full stellar radius. I.e. a is not far from the mass center, but not normally exactly at it.

Once the thermal instability at a is well developed, the temperatures, in this “hot spot” is higher than at the mass center and the dominate mode of energy transfer out of this hot spot is radiation, not conduction. The radiation pressure is likely to be a significant part of P(a). (Just guessing as I have no data.) Perhaps the best way to think of this “thermal runaway region” is a radiation filled bubble of relatively low mass density when the formation of iron abruptly terminates for lack of “fuel ion” density.

Without the constant fusion release of energy, the expanding radiation sphere, will quickly cool and the relative high mass density region just outside the “radiation bubble” will begin a radial collapse towards the off mass center point at a, where the first black hole will form. This rapid release of gravitational energy with the formation of black hole, not exactly at the mass center, will send a very powerful compressive shock wave into all near by parts of the star, including a front compressing the already much higher density region r < a. Even if these more central and denser regions were not yet quite ready to make black holes they will be “pushed over the edge” by the compression shock and more black holes will form, each generating additional compressive shock waves. When some of these "secondary shocks" collide, compressing even regions that were not close to the density required for forming a black hole, especially if compressing "from both sides," these regions too may form "tertiary black holes" and more shocks. - Sort of a chain reaction forming a multitiude of "solar size" black holes, all being hurled into space along with a great mass of very hot gases, which may even reform a lessor star and form a few more "solar size" black holes, much later.

SUMMARY: In essence, it seems plausible that the lack of the spherically symmetric collapse onto the mass center ASSUMED by the standard analysis, despite all the observational evidence that the collapse is not spherically symmetric, can give birth to a multitude of smaller “solar size” black holes, not the single big monster black hole the standard calculations predict for the collapse of a typical generation III star.
Hi Billy, I'll just sumarie my objections one last time.

While I think the idea of asymmetries in the collapse of stars is interesting and deserves some attention, I do not think that solar mass (or smaller) black holes can generate enough mass to account for all of the dark matter. The energy stored in dark matter represents about 10 times the amount of energy stored in all of the visible matter in the universe today. While one may expect some stellar mass black holes, I don't feel that there is nearly enough of them to make up 25% of the universe!

We never really debated your monopoles idea, but I can tell you that any relics like monopoles would have been inflated away in the very early universe. Sorry I haven't had time to properly look at this, but I have been quite busy these past few weeks. If I ever have time in the future, I will revisit this discussion.
.The energy stored in dark matter represents about 10 times the amount of energy stored in all of the visible matter in the universe today. While one may expect some stellar mass black holes, I don't feel that there is nearly enough of them to make up 25% of the universe!
To also summarize my reply to your POV: (1)perhaps monopoles do make up part of the dark matter or (2) if DM is to be only "stellar size black holes," then perhaps the mass of the generation III stars was 10 times larger than you think it was so now 90+% of that original mass is in undetectable stellar sized black holes. I am suggesting each of the first generation very large stars made dozens of these small black holes. Perhaps even most have left nothing visible now - just cold nebulae and small black holes. I prefer anything more consistent with Occam's POV than postulating some new form of matter.