Black holes so big we don't know how they form could be hiding in the universe

Jul 27, 2020
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One of the more likely sources for such large black holes is from the direct collapse of dense clouds. These BHs are postulated to have formed in the very early universe and could range from the very large to the very small. These are better known as primordial black holes - PBHs (1). They would form in much the way stars do, but the density is so high in certain regions that a BH can form without a stellar intermediate, simply by direct collapse formation.

As the article noted:

"Perhaps the first, and largest, black holes didn't come from the deaths of massive stars. Maybe they formed directly from the collapse of gas clouds, or from exotic processes in the early universe."

end quote

This would fit the requirement If the mechanism of direct collapse is involved. Again, the range of PBHs could be nearly infinite in such a mechanism. Another article recently appearing on this site addresses intermediate size black holes observed from a recent merger (2), and includes speculation as to their origins, since one is bigger than most models suggest it should be.

And everyone knows that models do not always end up being the final word in science......


1. https://en.wikipedia.org/wiki/Primordial_black_hole

2. https://forums.livescience.com/threads/largest-black-hole-collision-ever-detected.3492/
 
Jan 3, 2020
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The arxiv paper, which I note now has been formally peer reviewed with the help of Sutter, describes current super massive black hole observations that lie an order of magnitude lower than known black hole physics allow at the most. The rest of the paper is devoted to primordial black holes, of which none have been seen and I think none now is expected, and detection by weakly interacting massive particles which again hasn't been seen and expectations therefore are decreasing.

Black holes is not a boring subject, but this paper managed to poke a dark corner among speculation.
 
Jan 3, 2020
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This would fit the requirement If the mechanism of direct collapse is involved. Again, the range of PBHs could be nearly infinite in such a mechanism. Another article recently appearing on this site addresses intermediate size black holes observed from a recent merger (2), and includes speculation as to their origins, since one is bigger than most models suggest it should be.
There is a bit of a jump between a black holes mass estimate and a putative mass gap to primordial balck holes.

To take the obvious first, the large 85 (-14 +21) solar mass black hole lies ~ 1.5 sigma from the approximate 65-120 solar mass gap range, so there isn't a 5 sigma tension and it could be part of a 3 sigma confirmation in case the mass gap exist.

The mass gap models seems to have huge uncertainties due to difficult and speculative models of pair production collapse versus possible supernova results instead of a black hole. From the accompanying "properties and implications" paper: "Based on these considerations, ∼60–65 [solar mass] is probably a conservative lower limit to the edge of the mass gap."

And on the analysis on cluster hierarchical mergers: "In summary, the probability that GW190521 is due to a hierarchical merger in a stellar cluster is strongly dependent on the properties of 1g BHs in such environments, primarily on their mass and spin distributions and on the cluster escape velocity. With significantly larger event samples it may be possible to disentangle the different model parameters; thus, similar, high-mass BBH mergers constitute a future laboratory for BH populations and dynamics in cluster environments."

But of course I am biased by my analysis in my first comment.
 
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Jul 27, 2020
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The rest of the paper is devoted to primordial black holes, of which none have been seen and I think none now is expected,
It is impossible to know even the presence, much less the origin, of any black hole without some form of known radiation to "find" them. This necessarily means that any BH, regardless of source, would be impossible to simply be "seen".

Indeed, the only way BHs are known to exist is their impact on objects we CAN observe by some telescopic means. Simply put, primordial black holes can never be ruled out, at least not by rational science. No empirical evidence has yet, and probably ever will eliminate their likely presence from the known universe.

The "father" of BHs, none other than Stephen Hawking himself, predicted that their smallest mass would be around 10E-8 Kg (1). To be sure, Hawking was not convinced BHs even existed in his early career, only to become their greatest adherent. It seems likely the same events will play out with PBHs. Denials followed by grudging acceptance.

This acceptance might begin with more data from BH mergers, demonstrating larger and larger BHs merging in the distant past. Once these are found, it will become increasingly more difficult for the real experts to deny the probable existence of PBHs, especially those at the largest scale.


1. https://en.wikipedia.org/wiki/Primordial_black_hole


 

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