Miguel Mostafa, an assistant professor of physics, was among hundreds of collaborating scientists who discovered that ultra high energy cosmic rays, the most energetic particles in the universe, likely come from black holes.
Mostafa, along with physicist and U. Dean of Science Pierre Sokolsky, postdoctoral research associate Patrick Younk and physics graduate student David Thomas were among 370 scientists and engineers belonging to a 17-nation collaboration that operates the $54 million Pierre Auger Observatory in Argentina. Undergraduates Joshua Schmeiser and Felix Lau also work on the project. Their findings were published in today's edition of the journal, Science.
Black holes form when stars collapse, creating gravitational pulls so strong that nothing, including light, can escape. Scientists believe the majority of galaxies have supermassive black holes, which have the mass of up to a few billion stars similar to our sun.
When matter is drawn into these supermassive black holes, it spews out various particles and electromagnetic radiation, from gamma and X-rays to ultraviolet, visible and infrared light, and radio waves. A galaxy with a compact center that is extremely, persistently bright in all or some wavelengths is known as an active galactic nucleus. Only a fraction of galaxies with supermassive black holes are active galactic nuclei.
Mostafa, a native of Argentina, said he and his colleagues were able to figure out where the particles came from by measuring where they hit the Earth and backtracking the trajectory.
While the particles are fairly rare, hitting any given square mile of Earth only once in a century, Mostafa and his colleagues recorded 77 particles on the 1,200 square mile field of detectors found at the Auger Observatory.
The collaboration found that of the 27 most energetic events, 20 come from the direction of the known locations of some of the 318 active galactic nuclei - within the Auger Observatory's field of view, Mostafa says.
If the cosmic rays were randomly hitting the Earth from all directions, only a handful of particles would have correlated with locations of black holes, he said. The researchers report there is less than a one-in-100 chance that the correlation between ultra high-energy cosmic rays and active galactic nuclei is random.
When an ultra high energy cosmic ray hits the Earth's atmosphere, a cascading effect takes place. One ultra high energy particle can create hundreds of billions of particles that eventually hit the ground, Mostafa said.
However, the particles had to be coming from relatively nearby locations in order for the particles to retain their astounding energy, he said.
The particles had to originate within a distance of 100 megaparsecs, which works out to 326 million light years or 1,920 billion billion miles. Billion twice is correct.
"This is our local neighborhood in cosmic terms," Mostafa said.
While the ultra high energy particles likely come from black holes, Mostafa said several questions remain, including exactly what the particles are and how they become so energized. The particles from outer space are 100,000 times faster than the particles sped up by the largest accelerators on Earth, Mostafa said.
To continue exploring the particles, he will help build an observatory in Colorado that is 10 times larger than the Auger Observatory.
"This is extremely exciting," he said. "We built the Auger Observatory to answer this question, and now we have. Working together with scientists from so many countries has been fun, and I look forward to doing it again."