Despite making up almost 85 percent of the total mass of the cosmos, scientists have no idea what dark matter really is. Now, a new study by a scientist from NASA's Goddard Space Flight Center in Greenbelt, Md., supports the idea that dark matter is made of primordial black holes that were created during the first second of our universe's existence.
The paper suggests that this theory fits with what we currently know of cosmic infrared and X-ray background glows, and it might explain the unusually high masses of merging black holes that were observed last year.
"This study is an effort to bring together a broad set of ideas and observations to test how well they fit, and the fit is surprisingly good," said Alexander Kashlinsky, an astrophysicist at NASA Goddard. "If this is correct, then all galaxies, including our own, are embedded within a vast sphere of black holes each about 30 times the sun's mass."
Kashlinsky analyzed the possibility that dark matter consists of a population of black holes similar to those detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO), which alter the distribution of mass in the early universe and create a fluctuation that leads to consequences that ripple across hundreds of million of years up to the formation of the first stars.
During the first 500 million years of the universe, dark matter remained unaffected by high temperatures due to the fact that it interacts through gravity. Scientists believe that during this time period, dark matter collapsed into clumps called minihaloes that then led to the accumulation of normal matter.
After the formation of minihaloes, hot gas fell towards them, creating dense pockets of gas that then collapsed on their own into the first stars. In Kashlinsky's paper, he suggests that if black holes make up dark matter, this process would take place at a faster pace and explain the cosmic infrared background (CIB) characteristics detected in his previous research.
In addition, as minihaloes continued to capture cosmic gas, their black holes would capture some, as well. Any matter that makes its way towards a black hole would heat up and create X-rays. The combination of infrared light from the first stars and X-rays from gas making its way into dark matter black holes would explain the relationship between the CIB's patchiness and the cosmic X-ray background (CXB).
"Future LIGO observing runs will tell us much more about the universe's population of black holes, and it won't be long before we'll know if the scenario I outline is either supported or ruled out," Kashlinsky said.
The findings were published in the May 24 issue of The Astrophysical Journal Letters.
