 In this chapter, we covered how supermassive black holes form in three phases. First, a gas cloud collapses into a supergiant star. This can take a few million years. Second, the star exhausts its supply of hydrogen and supernovas into a black hole, or a neutron star that grows into a black hole. That also takes a few million years. At this point, we have a new stellar mass black hole, referred to as a black hole seed. In the third phase, the seed grows by accretion to supermassive sizes. This phase takes hundreds of millions of years due to the Eddington limit on its growth that we covered earlier. Black hole mergers might play a small role in black hole growth. But lots of black hole mergers would produce large numbers of intermediate black holes. Yet, we can't seem to find any. Plus, the larger black holes get, the less likely they are to merge. Due to orbital energy and momentum considerations, they stabilize into a binary system around 3 million light-years apart. That's one parsec. Given that black holes form from stars, we can expect that the first black holes formed from the first stars. The lambda-cold dark matter timeline has the first supermassive stars forming around 150 million years after the Big Bang. This includes the photon epoch from 20 minutes to 240,000 years, when the universe was filled with a hot, opaque plasma of photons, protons, neutrons, electrons, and dark matter. Recombination from 240,000 to 300,000 years. When electrons reunited with protons, creating a sea of hydrogen and helium atoms. Photon decoupling from 300,000 to 370,000 years, when photons were freed to travel across the universe. And the dark ages from 370,000 to 150 million years, when the sky darkened as the expanding universe stretched the bright surface of last scattering radiation into the infrared range. During this time, the caustic process worked the dark matter into filaments, with the baryonic matter, hydrogen, and helium, tagging along. At the 150 million year mark, the dense clouds of cosmic gas in the filaments started to collapse under their own gravity, becoming hot enough to trigger nuclear fusion reactions between hydrogen atoms, creating the very first stars, some of which became the very first black holes. Here's a graph put together by the Sears team that shows how, starting with the first population 3 stars, a standard black hole seed would grow over time. Note that there wouldn't be any million solar mass black holes, until around 625 million years after the Big Bang. But Sears 1019 has 9 million solar masses, and existed just 570 million years after the Big Bang. Either the Big Bang timeline is wrong, or there's another way for supermassive black holes to form. Theories that stretch the Big Bang timeline abound, but none of them have gained much traction. But two new theories for early black hole creation are gaining support. One is called direct collapse black holes, and the other is called primordial black holes. We'll cover them both. As the name implies, direct collapse black holes are formed by the collapse of a massive cloud of gas just a few hundred million years after the Big Bang, but it doesn't go through a star formation phase. The key to the theory requires a mechanism to prevent the normal collapse of a cloud into stars. For example, you could have a massive gas cloud and a galaxy moving towards each other. If the formation of stars in the gas cloud is stalled by radiation from the incoming galaxy, the gas can instead be driven to collapse and form a disk and black hole. This massive black hole seed and its disk then merge with the galaxy to grow rapidly into a supermassive black hole. The Sears team developed the timeline for the growth of direct collapse black hole seeds, but no sooner than they were done, the James Webb and Chandra teams determined that UHZ-1's black hole had a mass of 10 million suns and existed just 450 million years after the Big Bang. Clearly this did not fit the direct collapse model timeline. This brings us to primordial black holes. Primordial black holes are black holes that form before the end of the Dark Ages, including all the way back to the original inflation period. Theories go from micro-black holes during inflation that evaporated to massive black holes created via the caustic process on dark matter during the Dark Ages. For our purposes, it's the latter that explains supermassive black holes being found by the James Webb Space Telescope just 450 million years after the Big Bang. The key to any theory about what happened before stars started to shine begins with measurements of key quantities we can observe today and extrapolating back to conditions that could reasonably have produced them. For primordial supermassive black holes, the key quantities are the current distribution of baryons across the visible universe, referred to as the baryon budget, and the quantum variations found in the cosmic background radiation we see all around us. Extrapolating back into the Dark Ages involves a deep dive into perturbation analysis on key energy and stress components of Einstein's field equations that are beyond the scope of this video book. This primordial black hole theory has it that during the Dark Ages, gravitational attraction associated with superdense concentrations of dark matter would collapse into massive primordial black holes. No accretion disk is involved, so no interaction between dark matter particles beyond gravity would be required. These would be primarily dark matter black holes that then grow on baryonic matter via accretion disks over 150 million years earlier than normal black holes, giving them time to reach the UHZ-1 and Sears-1019 masses at their early date. I personally like this idea because it is the simplest explanation for the early supermassive black holes and the galaxies around them without any Big Bang timeline changes. But it will take a lot more data collection and analysis by Webb and other telescopes to determine just how this all came to be.