The first black holes in the universe were born starving.
A new study found that the earliest black holes lacked nearby matter to gobble up, and so lay relatively stagnant in pockets of emptiness.
The finding, based on the most detailed computer simulations to date, counters earlier ideas that these first black holes accumulated mass quickly and ballooned into the supermassive black holes that lurk at the centers of many galaxies today.
"It has been speculated that these first black holes were seeds and accreted huge amounts of matter," said the study's leader Marcelo Alvarez, an astrophysicist at the Kavli Institute for Particle Astrophysics and Cosmology in California. "We're just finding out that it could be much more complex than that."
Alvarez and colleagues constructed a computer simulation of the early universe based on measurements of the cosmic background radiation left over from the Big Bang, which scientists think started the universe 13.7 billion years ago. The model used these starting conditions, and the laws of physics, to watch how the universe may have evolved.
The study is detailed in an upcoming issue of The Astrophysical Journal Letters. The Kavli Institute is at the Stanford Linear Accelerator Center (SLAC) National Accelerator Laboratory in Menlo Park, Calif.
Hungry, hungry black holes
In the simulated young universe, clouds of gas condensed to form the first stars. Because of the chemistry of the gas at this time, these stars were much larger than today's typical stars and weighed more than a hundred times the mass of the sun.
After a short time these massive, hot stars exhausted their internal fuel and collapsed under their own immense weight to form black holes. But because the huge stars had emitted such strong radiation when they were still alive, they had blown most nearby gas away and left very little matter to be eaten by the resulting black holes.
Rather than swiftly swallowing large chunks of matter and growing into larger black holes, the simulation showed that the universe's first black holes grew by less than one percent of their original mass over the course of a hundred million years.
The scientists don't know what eventually became of these hungry black holes.
"It is possible that they merged onto larger objects that then themselves collapsed into black holes, bringing these first black holes along for the ride," Alvarez told SPACE.com. "Another possibility is that they got kicked out of the galaxy by interactions with other objects and would just be floating around in the halo of the galaxy now."
Whatever happened, the researchers think that these trailblazing black holes may have played an important part in shaping the evolution of the first galaxies.
Even on a diet, the black holes likely produced significant amounts of X-ray radiation, which is released when mass falls onto a black hole. This radiation could have reached gas even at a distance and heated it up to temperatures too high to condense and form stars. Thus the first black holes may have prevented star formation in their vicinity.
These hot gas clouds may have carried on for millions of years without creating stars, and then eventually collapsed under their own weight to create supermassive black holes.
Though this idea is only speculation, the researchers are intrigued by the possible effects of the universe's first black holes.
"This work will likely make people rethink how the radiation from these black holes affected the surrounding environment," said John Wise of NASA Goddard Space Flight Center in Greenbelt, Md. "Black holes are not just dead pieces of matter; they actually affect other parts of the galaxy."
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