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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