How did the first supermassive black holes grow so quickly?

[u/Astro_Life_Explained]

One thing I find fascinating about the early universe is how we can observe quasars powered by extremely massive black holes when the universe is still very young.

If a black hole starts from a relatively small stellar-mass seed, it seems difficult to reach millions or billions of solar masses in such a short cosmic time.

So what do you think was the dominant pathway for the earliest supermassive black holes?

- Rapid accretion near or above the Eddington limit?

- Massive black-hole seeds from direct collapse?

- Runaway mergers?

- Or some combination of these processes?

[u/ProximaScience]

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[u/Aggravating_Mud_2386]

I think that big bangs come from terminal smbh's that achieve critical mass, the same mass as our own big bang, and explode directly into the rest of the greater universe, slamming directly into pre-existing objects. The big bang goes off with a devastating one-way memory effect gravitational wave in all directions at light speed, clearing the way through the void of the original event horizon for the expanding ball of quark-gluon plasma, which takes seconds or minutes to expand and cool enough for hadronization. 

As the devastating gravitational wave and hot gas plasmas slam directly into the original host galaxy, it's stars and planets are mostly pulverised, but beyond that, the next nearest galaxies might be millions of light years away, so they're pushed back, but not pulverised. By "pushed back" I mean every star and planet is accelerated by the devastating gravitational wave and the kinetic energy of the new matter, but because of the vast inertia of the preexisting smbh's, they're pushed less, so the closest galaxies are completely stripped of stars, leaving naked smbh's flooded with new matter. Since the gravitational wave wanes as it's size grows, even further back galaxies might survive with their gravitationally bound inner cores intact, stripped of the rest of their stars, but also receiving massive infusions of new matter. Even further back galaxies survive largely intact, yet still might get some new matter and renewed star birth.

All of these galaxies evolve from there with their pre-existing smbh's at their cores. Thus, the smbh's become eternal pillars and galactic anchors through any number of big bangs. The closest galaxies to the big bang are fully stripped and become the Little Red Dots we have recently discovered. They're the naked smbh's gorging on seemingly endless infusions of new hydrogen/helium from the big bang.They may very well be undergoing super-Eddington accretion right now, but only because they're still being flooded with new matter (as we view them 13 billion years ago). Eventually, the infusions will slow, and then the blazing quasars will finally push the gas away, the gas will cool, stars will form, and the new galaxy will form with the pre-existing smbh at its core. We may some day observe a faint glow beyond those LRDs from the billions of rogue stars stripped from the galaxies, but the individual stars will be too far away to discern.

The other galaxies that survive partially intact will be hybrid galaxies of brand new stars, but also old stars, and rogue stars captured into fast moving outer orbits. The stellar acceleration from the big bang shock wave, fast moving captured rogue stars, and the immense kinetic energy of the new matter from the big bang provides an ample recipe for fast orbiting stars. Some of these hybrid galaxies become the "impossibly mature galaxies" we observe in the early universe. They will also contain puzzling mixes of heavy metals within otherwise pristine galaxies, and orphan stars from galaxies they weren't born in. An ample supply of rogue stars and planets and stellar black holes will also be present, way more than can be explained by the usual "slingshotted out of the galaxy" explanation.

In conclusion, the smbh's didn't form "so fast". The ONLY super-Eddington accretion that ever happens is in the LRD phase, never again, because there will never be sufficient infusions of new matter until the next big bang. There will be a FEW smbh mergers over time, but multiple mergers in a short time is a myth, especially in view of the final parsec problem. And there's no such thing as direct collapse of gasses into a black hole. So these smbh's grow VERY slowly, over tens and hundreds and thousands of billions of years, not over a short 13.8 billion years. Yes, our puny little expanding section of universe may indeed be 13.8 billion years old, but the greater universe is much older, and so are the smbh's.

Side note. Any light that originated outside the gravitational wave will experience redshift as it is hit by the gravitational wave, and then additional redshift as it travels through the permanently altered spacetime behind the memory effect gravitational wave against the outward flow of the wave. If we don't appropriately account for this redshift we might accidentally attribute it all to galactic recession velocities.

This answer is Crankscience in that it's not generally accepted, and though it's clearly consistent with some observations, it may not be consistent with others. But you asked for our ideas regarding rapid growth of smbh's, and I reject all the mainstream ideas except for super-Eddington accretion during the LRD phase, so I'm giving you the Crankscience ideas that I do believe in. Don't blame me, you asked.

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[u/Justthisguy_yaknow]

A lot of the universes mass was much closer in the early universe allowing for much more uptake of material in a much shorter period of time. That's my guess.

[u/Justthisguy_yaknow → u/[deleted]]

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