"It has been the goal of much of ultrahigh-energy cosmic ray physics for the past 40 years to find this cutoff or disprove it," says physics Professor Pierre Sokolsky, dean of the University of Utah College of Science and leader of the study by a collaboration of 60 scientists from seven research institutions.
Last November, the Auger observatory collaboration - to which Sokolsky
also belongs - published a study suggesting that the highest-energy cosmic rays come from active galactic nuclei or AGNs, or the hearts of extremely active galaxies believed to harbor supermassive black holes.
"We still don't know where they're coming from, but they're coming from far away," Sokolsky
"Quite apart from arcane physics, we are talking about understanding the origin of the most energetic particles produced by the most energetic acceleration process in the universe," Sokolsky
Sokolsky and University of Utah physicist George Cassiday won the prestigious 2008 Panofsky Prize for developing the method.
says there is debate over whether the "ankle" represents cosmic rays that run out of "oomph" after being spewed by exploding stars in our galaxy, or the loss of energy predicted to occur when ultrahigh-energy cosmic rays from outside our galaxy collide with the big bang's afterglow, generating electrons and antimatter positrons.
The Telescope Array
and Auger observatories will keep looking for the source of rare ultrahigh-energy cosmic rays that evade the big bang afterglow and reach Earth.
"The most reasonable assumption is they are coming from a class of active galactic nuclei called blazars," Sokolsky
Such a galaxy center is suspected to harbor a supermassive black hole with the mass of a billion or so suns.
As matter is sucked into the black hole, nearby matter is spewed outward in the form of a beam-like jet.
When such a jet is pointed at Earth, the galaxy is known as a blazar.
"It's like looking down the barrel of a gun," Sokolsky