Finally, astronomers understand why black holes grew so rapidly to become so large.

“Computer visualization showing baby black holes growing in a young galaxy from the early Universe. Credit: Dr John Regan” (ScitechDaily, Astronomers Solve the Mystery of How Black Holes Got Big So Fast)

In a young, chaotic universe, the first primordial black holes were small. They formed straight from radiation. Or radiation-particle interaction. Those small primordial black holes formed in a universe that was denser. And that was. In a higher energy level. So, when somewhere in that hot universe, a black hole. That thing had more material and energy than in the modern universe. That it  could pull inside it. That matter and energy feed the black hole. That caused a situation. Where those black holes could grow very fast into supermassive black holes. 

Black holes form in the ultra-high-energy reactions in the universe. Or, actually. Those black holes form just after the supernova explosion. The energy that the star releases in the supernova explosion forms a bubble. Small cosmic void. Only a very heavy star can form a black hole. When that void starts to collapse, it crushes matter into a very dense form. And if that impact energy is high enough, it pushes matter, subatomic particles, and quantum fields into the one entirety called a singularity. 

In cases where the black hole forms in quark-gluon plasma (QGP or quark soup). That thing can raise its mass very fast. The quark-gluon plasma  formed just after the Big Bang. There formed whirls in a high-energy radiation field. The reason for that was that a space allowed the superstring’s vertical and horizontal movement. In this model, the radiation that left from the Big Bang was first coherent. But then. A free space formed in the energy field. 

Those whirls pulled so-called superstrings inside them. In that case, the Schwinger effect formed the first particles. In that space, even a micro black hole can grow its mass rapidly. And the most important question in modern cosmology is this: Which came first: particles or black holes? The model is that. The black hole can form straight from quantum fields or radiation. Those Kugelblitz back holes could form just after the Big Bang. But did they form in quark-gluon plasma or before, or after that stage? 

The minimum mass of the black hole. The Tolman-Oppenheimer-Volkoff (TOV) limit is about 2-3 suns. When a supernova explosion happens, part of the star’s mass escapes into the universe. And that means the star’s mass must be about 5 times higher than the Sun’s mass. The mass of the supernova remnant must be so high that the neutron star collapses. That is one way to handle black holes. But the TOV equation is made for the modern universe. 

But then. We must realize that in the very young and chaotic universe, the small primordial black holes formed the mass centers. Actually, even at the beginning of the universe, when the first quarks or electrons formed. It is possible that energy travels in the electron, or some other ball-shaped object. Then the energy jumps back from inside that quantum ball. That effect can form the cosmic microvoid, which collapses. That forms a miniature black hole. Which starts. To pull energy and matter from around it. If that happens in the quark-gluon plasma, that thing can start the formation of the supermassive black holes very fast. In quark-gluon plasma, energy and matter were in a far denser formation. In those conditions, even a small black hole can grow very fast.  

https://scitechdaily.com/astronomers-solve-the-mystery-of-how-black-holes-got-big-so-fast/

https://en.wikipedia.org/wiki/Kugelblitz_(astrophysics)

https://en.wikipedia.org/wiki/Micro_black_hole

https://en.wikipedia.org/wiki/Quark%E2%80%93gluon_plasma

https://en.wikipedia.org/wiki/Tolman%E2%80%93Oppenheimer%E2%80%93Volkoff_equation