On Saturday, November 7, 2020 at 6:27:34 AM UTC-6 [email protected] wrote:
> 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 will have to read this paper so as not to talk at cross purposes. It is a bit odd, for it appears to reference gravity lenses more than microlenses. Microlenses occur when a star "winks" because a gravity field passes in front of it. It is my understanding, which is not terribly deep in astronomical methods, that primordial BHs is now a minority report. LC > > 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/d142efc5-6a92-4f4a-ad9b-0a3dfc874603n%40googlegroups.com.
