PORTLAND, Ore. -- Dark matter and dark energy comprise 96 percent of the universe, or so says the "standard" theory; but where (and what) are dark matter and dark energy? Scientists call them "dark" because their presence has to be deduced from gravitational data about the visible universe, which indicates the presence of 74 percent more energy, and 22 percent more matter, than we see through our telescopes. Just this year, however, newly proposed theories have offered new explanations of dark energy and dark matter. Dark energy, for instance, was recently explained as the quantum "pressure" of empty space and dark matter as located in a halo around the galaxies. Now, researchers at the University of Utah (Salt Lake City) have an explanation for how dark matter, powered by weakly interacting massive particles (WIMPs), enabled the creation of vast dark stars.
"Dark stars are clouds of heavy, stable particles 400 to 200,000 times larger than normal stars," said astrophysicist Paolo Gondolo, associate professor of physics at the University of Utah. "They were formed 80 million years after the Big Bang [in places] where neutralinos were annihilating anti-neutralinos, thereby providing enough heat to prevent the hydrogen and helium clouds from cooling and condensing into regular stars, [thus creating] vast dark stars."
Dark stars take up such large areas that no one has looked for their telltale infrared glow. They formed 80 milion yeas after the Big Bang, which produced both neutralinos and anti-neutralinos, akin to matter and antimatter. The conjunction of the two annihilates both, producing telltale signs that include gamma rays, neutrinos and antimatter emissions accompanying clouds of cold, molecular hydrogen gas that normally wouldn't harbor such energetic particles.
"After the Big Bang, there was a big halo of dark matter and anti-dark matter that gravitationally became denser and denser until dark stars condensed: dark because they were not hot enough to ignite. But when dark matter and anti-dark matter annihilated each other, producing subatomic particles called quarks and their antimatter counterparts, antiquarks, that generated heat, which kept the normal hydrogen and helium from cooling and shrinking. These vast dark stars could still be out there," said Gondolo.
Currently, Gondolo's group, which includes astrophysicist Katherine Freese of the University of Michigan, Ann Arbor, and graduate student Douglas Spolyar of the University of California, Santa Cruz, is advising astronomers to look for vast dark stars emitting infrared radiation in globular clusters and in the centers of old galaxies.
The work was funded by the National Science Foundation, the U.S. Department of Energy and the University of Michigan.