“Which came first: the galaxy or its monstrous black hole?”
Technically, it’s an even older riddle than the chicken or the egg, even though we only became aware of it relatively recently. And according to new research, scientists may finally have an answer.
It has long been believed that supermassive black holes that existed close to the beginning of time formed the galaxies around them, accelerating star formation in the galaxies and thereby affecting the evolution of the entire universe. But now a reanalysis of data from the James Webb Space Telescope (JWST) indicates that these black holes could have been present for the first 50 million years of our 13.8 billion-year-old universe, causing star formation at such a young age.
The findings may challenge the idea that only black holes formed after the first stars and galaxies emerged.
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“We know that these monstrous black holes exist at the centers of galaxies near our Milky Way, but the big surprise now is that they were also present at the beginning of the universe and were almost like building blocks or seeds for early galaxies,” says Joseph. Silk, team leader and professor at Johns Hopkins University, said in a statement. “They’ve really supercharged everything, like giant amplifiers of star formation, which is quite a turnaround from what we previously thought possible — so much so that this could completely shake up our understanding of how galaxies form.”
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Silk points to the fact that distant and early galaxies the JWST has been looking at have been brighter than expected since it started sending data to Earth in the summer of 2022.
This suggests that the galaxies are already packed with unusually high numbers of stars and supermassive black holes; If true, it would mean that our current theories about how galaxies grow may need to be revised.
“We argue that a black hole ejects crushed clouds of gas, turning them into stars and greatly accelerating the rate of star formation,” says Silk. ‘Otherwise it is very difficult to understand where these bright galaxies come from, because they tend to be smaller in the early universe. Why on earth would they need to make stars so quickly?’
Currently, the most widely accepted theories of cosmic evolution suggest that black holes formed in the early universe when very massive stars ran out of fuel needed for nuclear fusion. In turn, those stars would have collapsed in later eras of the universe, creating black holes. This means that the black holes must have formed after the formation of the stars from which they emerged, and also before the first mergers of galaxies.
Yet Silk and colleagues found that black holes and galaxies appeared to have coexisted during the ancient universe, influencing each other as early as 100 million years after the Big Bang. This period, Silk says, would be equivalent to just the first days of January if the history of the universe were condensed into a calendar year.
The crushing in the early universe
The immense gravitational influence of black holes means that nothing (not even light) can escape the outer boundary, known as the event horizon. What this means for us is that anything outside that boundary is not immediately visible.
But beyond the event horizon, things still happen. A black hole’s gravity is still intense enough to create violent conditions for surrounding matter, with the misfortune of falling too close to the event horizon, heating it and causing it to flow brightly. This matter can be swallowed, or can be channeled to the black hole’s poles, where it is blown out at near-light speeds as jets or winds.
Black holes that actively feed on such matter can power so-called active galactic nuclei (AGN), or regions within galaxies that can outshine the combined light of every star in the galaxies themselves.
Silk thinks that the fact that black holes behave like “cosmic particle accelerators” in this way allowed the JWST to discover so many of them in the early universe.
“We can’t see these violent winds or jets quite far away, but we know they must be present because we see a lot of black holes early on in the universe,” Silk explains. ‘These huge winds coming out of the black holes crush nearby gas clouds and turn them into stars. That is the missing link that explains why these first galaxies are so much brighter than we expected.’
The universe was going through a phase (or two).
The team behind this research theorized that the early universe had two distinct phases. In the first phase, the rapid outflow of black holes would have accelerated the birth of stars. The second phase would have begun when this outflow ceased.
After this, when the universe was about a few hundred million years old, huge gas clouds would have been forced to collapse due to intense magnetic storms caused by supermassive black holes. This would have triggered a new period of intense and rapid star formation that far exceeded the birth rates of more modern galaxies.
Star formation would then be hampered because the massive outflow of supermassive black holes would have entered an energy-conserving state, cutting off the gas supply to galaxies where stars could form.
“We thought that galaxies initially formed when a giant gas cloud collapsed,” Silk explains. ‘The big surprise is that there was a seed in the center of that cloud – a big black hole – and it helped the inner part of that cloud quickly turn into stars, at a rate far greater than we ever expected. And so the first galaxies were formed. are incredibly bright.”
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Not only does the team think that future JWST data could provide more accurate early numbers of stars and supermassive black holes that will confirm the new theory, but the researchers also believe that the $10 billion space telescope could provide some answers to fundamental questions closer to home lie.
“The big question is: what was our beginning? The sun is one star in 100 billion in the Milky Way galaxy, and there’s also a huge black hole in the middle. What’s the connection between the two?” Silk concluded. “Within a year we will have so much better data and many of our questions will be answered.”
The team’s research was published in January in the Astrophysical Journal Letters.