On Fri, Nov 6, 2020 at 8:18 PM Lawrence Crowell < [email protected]> wrote:
*>>> If the entropy of the early universe were too large the current >>> universe would be very different. In fact with black holes, if there were >>> too many primordial BHs the universe would contain little other than BHs.* >>> >> >> >> Maybe to a first approximation the universe does contain very little >> matter except for primordial black holes if black holes turn out to be dark >> matter, or at least a substantial part of it. I'm not saying it's true >> I'm just saying it's possible. John K Clark >> > > > That has largely been ruled out. By looking for microlensing it appears > dark matter is less than 1% due to primordial black holes. > I don't know if the idea is correct but I don't think it can be dismissed that easily, I don't think the evidence to support the conclusion that Primordial Black Holes being responsible for Dark Matter can be ruled out has been universally accepted as being sound. Evidence from microlensing against Black Holes being responsible for Dark Matter is strongest for them being greater than 100 solar masses, and the evidence from the cosmic microwave background radiation against them is strongest for Black Holes of less than 5 solar masses. It is precisely in that 5 to 100 solar mass gap that LIGO has found far more Black Holes than had been expected. A recent paper argues that the probability visible stars in a lensing galaxy could be responsible for all the observed microlensing is very small and concludes with: *" the most plausible candidates for the microlenses are primordial black holes, either in the dark matter halos of the lensing galaxies, or more generally distributed along the lines of sight to the quasars and the recent detection of gravitational waves attributed to a black hole merger supports this idea. It is possible that dark matter in the form of primordial black holes in the lensing galaxy halos are responsible for the observed microlensing, but it is not clear that they would constitute a sufficiently large optical depth to microlensing. A more plausible possibility is that the microlensing is the result of a cosmological distribution of dark matter primordial black holes along the line of sight to the quasar images."* The signature of primordial black holes in the dark matter halos of galaxies <https://arxiv.org/pdf/2001.07633.pdf> Also, without Primordial Black Holes it is difficult to explain LIGO's discovery of a 66 and 85 solar mass Black Hole merger that occured 7 billion years ago because stars in that mass range can't produce them. Stars in the 65 to 135 solar mass range would end their lives in a Pair-instability Supernova, the most powerful type. The core of such stars would reach temperatures of about 300 million Celsius and the photons of light produced would be so energetic they would spontaneously convert into electrons and positrons which would reduce the radiation pressure and cause the core to collapse making it even hotter and instantly causing the fusion of every element in it that was lighter than Iron. This would completely blow the core apart leaving nothing behind, not a Neutron Star not a Black Hole nothing. Stars greater than 135 solar masses wouldn't produce a supernova at all, they would just collapse directly into a Black Hole and suddenly shut off, but stars that big are very rare, especially when you consider that they must've been in the 250 solar mass range when they started their lives because such stars give off huge amounts of matter as solar wind before they reach the end of their lives. Primordial black hole dark matter and the LIGO/Virgo observations <https://iopscience.iop.org/article/10.1088/1475-7516/2020/09/022> And of course it could be that Primordial Black Holes make up part of Dark Matter and something completely unrelated makes up the other part, or the entire idea could just be wrong. Time will tell. John K Clark -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/CAJPayv3WmCNG64EpyXJrEoVK%2Bbz%3D70asRKdB-PJ30uZt21D5BQ%40mail.gmail.com.
