Black holes aren't just cosmic destroyers or grim reminders of the final fate that awaits massive stars. They may have once had a more constructive purpose. New models suggest they were essential in the formation of the early universe.
The 2003 discovery that black holes not only existed 13 billion years ago but were in fact commonplace posed some baffling questions for cosmologists. Even if it were possible to account for how black holes came to exist in such numbers less than a billion years after the Big Bang, that still left the issue of how precisely their existence affected the development of the young cosmos.
Researchers at Stanford's Kavli Institute for Particle Astrophysics and Cosmology took a giant leap towards an answer last August, when they ran a supercomputer simulation of the universe's formations. The simulation suggested that, 200 million years after the Big Bang, unbelievably gigantic stars began to form, roughly a hundred times the size of our sun. Such stars lasted just a few million years before exhausting their fuel and collapsing in on themselves, creating the first black holes.
Though born of stellar behemoths, these black holes were quite tiny, and they grew slowly because the massive supernovas that preceded their formation had blasted away almost all nearby matter. Still, even though their mass increased by an average of just one percent over the next 200 million years, these black holes wielded tremendous cosmic influence. The black holes managed to attract just enough matter to release radiation that in turn heated the surrounding clouds of gas. The clouds began to boil at around 5,000 degrees Fahrenheit, too hot to readily allow for stellar formation. This effectively controlled and limited the star population during the universe's first billion years.
This, however, is only the beginning of the story. 2007 saw the discovery of a black hole with a billion times the mass of the sun that existed a mere 840 million years after the Big Bang. The situation only got weirder last September when astronomers discovered a large galaxy not unlike our own formed around the black hole. This was a vastly different situation from the one suggested by Stanford's supercomputers, and less than 500 million years had elapsed between the two states of affairs.
Yuexing Li, an astrophysicist at Penn State, is tackling this question by looking at larger structures and processes in the early universe. The first black holes, roughly 100 times the mass of the sun, were surrounded by dense clouds of matter that were another 1,000 times more massive. These arrangements constituted the first protogalaxies. Cosmic movement brought these protogalaxies into violent collision with each other, merging the black holes together into a single larger black hole.
Li's model suggests that such interactions could create a billion-solar-mass black hole within 800 million years, and in particularly crowded regions of the early universe this process could have occurred even more quickly. She estimates that the first of these supermassive black holes could have emerged as little as 500 million years after the Big Bang, which would comfortably allow for the black hole spotted in 2007.
Moreover, these black hole collisions were the engines of creation for the first true galaxies. The shockwaves of merger would have compressed the surround clumps of gas, creating conditions more favorable for star creation. Thus, the first billion years of stellar and galactic formation are deeply intertwined with the earliest black holes.