Swarms of 'primordial' black holes might fill our universe

Jul 27, 2020
One of my favorite theories is getting its own article - Primordial Black Holes - right here on LiveScience (so much to be thankful for!!). These PBHs (1,2,3) have been postulated for many years, but largely dismissed for various reasons. Pretty much the way all the experts dismissed fission and prions before they were proven facts.

Whenever I have brought up PBHs in a forum anywhere, people would pile on and tell me it was insane, and that I should stick with biochemistry - au contraire! Most of the high brows in cosmology think they have it all figured out, except the minor details, like dark matter and dark energy.

So many are the times we have been told that PBHs were not possible. Even disproven, of all things! You get the picture. It happens all the time to contrarians. We can take it until the cows come in, or the PBHs are confirmed (since they can never be ruled out).

But now there is much greater interest following the detection, by Gravitational Wave Astronomy (4), of intermediate size black holes, with some approaching 100 solar masses. They should not be so large based on their expected formation from core collapse supernova, or even from the merging of smaller black holes (from that same source). And they are going to see more and more of them. Our detection of a few of them in short data collection periods means there are a lot of them going on! Let's watch as the size of these merging BHs increases.

Now, of course, some are reviving the potential of PBHs as a dark horse candidate for dark matter (1,2). It should be appreciated that Steven Hawking predicted this very notion back in 1971. He estimated a miminal mass of a PBH at about 10E-8 kg.

If small PBHs can form, there is no theoretical limit on their size. Meaning they could very well result in the formation of super massive black holes (SMBHs), either directly or by mergers (5,6). SMBHs are at the core of nearly all galaxies, with many containing billions of solar masses.

SMBHs are postulated by most to form from countless mergers of large black holes created by Population III stars within the first billion years after the Big Bang. It certainly is possible that this mechanism produced many large BHs. After all, there is no data to disprove the existence of such massive stars. But they do not exist in the observable universe, unlike these unexplained intermediate size BHs. They certainly exist based on Gravitational Wave Astronomy.

So to be perfectly blunt : PBHs are still in the running for explaining a lot of things, from galactic SMBHs to dark matter. Some are even postulating that a "Planet 9" could be a PBH with an event horizon the size of a grapefruit (7). Others have even postulated that evaporating PBHs could be a source for dark energy in the early universe (8).

So there could be more than enough PBHs for everyone, no pushing or shoving required. Keep a watch on this story. It may very well re-write some core concepts of the Big Bang, and the very nature of the Universe.

"Primordial Black Holes as a dark matter candidate"
1. https://arxiv.org/abs/2007.10722

"Primordial Black Holes as All Dark Matter
2. https://arxiv.org/abs/1001.2308

"Primordial Black Hole"
3. https://en.wikipedia.org/wiki/Primordial_black_hole

"Gravitational-wave astronomy"
4. https://en.wikipedia.org/wiki/Gravitational-wave_astronomy

"Primordial Black Holes as Dark Matter: Recent Developments"
5. https://www.annualreviews.org/doi/abs/10.1146/annurev-nucl-050520-125911

"Formation and evolution of primordial black hole binaries in the early universe"
6. https://iopscience.iop.org/article/10.1088/1475-7516/2019/02/018

"Is Planet 9 Actually A Primordial Black Hole?"
7. https://www.forbes.com/sites/brucedorminey/2020/07/11/is-planet-9-actually-a-primordial-black-hole/?sh=78a232374d80

"Evaporating primordial black holes as varying dark energy"
8. https://www.sciencedirect.com/science/article/abs/pii/S2212686419301967
Last edited: