[FRIAM] primordial or primeval?

[David Eric Smith]

Yes, good questions, and because I am far outside this field, I can parrot things I have been told, but not check against any adequate understanding of my own.

> On Jun 29, 2022, at 12:04 AM, glen <gepropella at gmail.com> wrote:
> 
> Very helpful. So for primordial objects, it sounds like we'd be looking for flashes in an otherwise/almost ambient field, as opposed to distortions of an otherwise steady/bright object.

I think, for microlensing, that the distribution of BHs transiting in front of something would be about as uniform as any of the rest of the clustered matter around at the same time-depth (redshift).  A wider object (like a galaxy nearby enough that you can see it as having angular width) should (I assume) be harder to see lensed with a single BH, just because the BH would be small compared to what you can already see, so wouldn’t add much light.  Something dot-like would be easier to identify, because the BH would be gathering a little more light in your direction that would otherwise have shined to one side or the other of your telescope.  But the dot could be an isolated star if not too far away or not in too dense a field, or a galaxy if much further away.  I do wonder if the middle-distance, where most of what you can see are resolvable galaxies, is a kind of observational desert just because of the method limitations; a microlensing expert could tell us.  Maybe one compared pixel by pixel in the image.

> If we find too few (scaling up however for estimates of the unobserved), then it's evidence against. What I was wondering was more around the sizes. The primordial ones must be smaller, I'd guess.

What was said to me is that the primordial ones from early matter-density fluctuations would have become around solar-mass fairly early on.  But the expansion of the universe at that time would have been so fast that it would have created fairly wide separations among them quickly, making them a kind of quasi-uniformly-distributed dust in the sky.

> But they'd have to be everywhere at first (most distant), then clumping together over time (closer).

This statement sounds exactly like my understanding of the assertions.

> And I can't help but wonder if the anisotropic clumping could explain those puffy galaxies light on dark matter.

Yeah, nice connection.  Goes beyond what I know, so I can’t offer anything back.

Eric



> 
> I can't muster empathy to the disappointment in reconciling the particles with gravity, though. 8^D I'm too much of an outsider, I guess ... like the new marketing suit touring the server room having no idea what he's looking at but marveling at the cables, and the hum, and the Morlocks tapping away. The pictures on 7/12 are guaranteed to be pretty, regardless of what they mean.
> 
> On 6/27/22 13:29, David Eric Smith wrote:
>> What a great shot in the arm to start a morning.
>> I just got back from a small conference in Groningen, which turns out to be (I didn’t know) a kind of fountainhead for large-scale structure cosmologists.  So got some much-needed remedial education on the topics in Glen’s links below.
>> I asked one guy what was the bound on how many black holes could have been produced early, given what we know today, thinking (in my near-total ignorance) that it would be collisions reported with the LIGO et al. collaboration.  His answer mentioned something I didn’t see in these articles, which was that microlensing counts are likely to provide some of the best bounds on the primordial black holes if they are to be dark matter candidates.  This is when a telescope is looking at some distant dim dot, and it briefly flickers brighter because a black hole passed between it and us, and lensed in a tiny bit more angular sector of its light.  I guess Webb contributes to those counts too (if I didn’t create a further mis-understanding).
>> The idea that all of dark matter could be accounted for with nothing but black holes is strangely both tempting and disappointing.  Tempting in that, in the short term, it would explain a phenomenon, and check one more off the list.  Disappointing in that, if we could close _everything_ we can observe with just the low-energy standard model and general relativity, then we have no clues what to do to make them consistent.  If there were at least some phenomena that we could show were _sure_ to be beyond explanation with the existing models, we could at least hang a hope on there's being some signature to lead into this very deep high-energy wilderness that, for now and maybe indefinitely, we can’t reach in any lab on Earth.
>> Good stuff,
>> Eric
>>> On Jun 27, 2022, at 11:39 PM, glen <gepropella at gmail.com> wrote:
>>> 
>>> I'm guessing "primordial" carries the foundationalist urge, whereas "primeval" is more agnostic to foundations, but targets sequence. So the test for hypothesis is simply *if* Webb finds no evidence of small black holes, then the they can't account for dark matter. Right? Or is there something more subtle about it? ... mabye something "distributional"?
>>> 
>>> Black holes and dark matter — are they one and the same?
>>> https://news.yale.edu/2021/12/16/black-holes-and-dark-matter-are-they-one-and-same
>>> 
>>> Webb’s Quest for Primeval Black Holes
>>> https://blogs.nasa.gov/webb/2022/05/26/webbs-quest-for-primeval-black-holes/
>>> 
>>> And maybe tangentially,
>>> 
>>> Astronomers identify likely location of medium-sized black holes
>>> https://phys.org/news/2022-04-astronomers-medium-sized-black-holes.html
>>> 
>>> P.S. July 12th:
>>> First Images of the James Webb Space Telescope (Official NASA Broadcast)
>>> https://youtu.be/nmMRMIE3MGw
> 
> 
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