Active Galactic Nuclei May Not Be the Source of Cosmic Rays

No more than three years ago, experts using a large telescope array in Argentina published a paper proposing a possible source for the peculiar space phenomena that are cosmic-rays. This type of radiation is composed of highly-energetic particles, whose origins are a complete mystery. The investigators said in 2007 that Active Galactic Nuclei (AGN) might be at the origin for cosmic rays, but now the same astrophysicists find themselves in the awkward position of casting doubt on their own work. New observations do not appear to support their previous conclusions, Nature News reports.

Inside AGN, supermassive black holes power up giant cosmic particle accelerators, which scientists have for a couple of years believed to be the way cosmic rays are produced. When these particles were connected to the black holes, in the 2007 paper, the astrophysics community was thrilled. “We thought a new astronomy had been born: charged particle astronomy,” explains US Naval Research Laboratory (NRL) cosmic-ray astrophysicist Charles Dermer. But recently, the same team that published the results threw considerable doubts on it.

The group, from the Mendoza, Argentina-based Pierre Auger Observatory, presented their latest findings on February 16 in Washington DC, at the annual meeting of the American Physical Society (APS). They revealed that the connection between AGN and the highly-energetic particles was a lot weaker than initially estimated, and also that the radiation they observed might actually be made up of iron nuclei, rather than the protons astrophysicists know make up cosmic-rays. “There are some puzzles. We're not close to writing the final chapter,” says Pennsylvania State University spokesperson Paul Sommers adds.

The old results are also disputed by a team operating the High Resolution Fly's Eye (HiRes) experiment in Utah, which says that ten direct cosmic ray observations appeared to indicate varied sources for the radiation, not necessarily tied to the directions of AGN. Additionally, the US-team also found that the rays were made of protons and not iron nuclei, which is yet another difference from the findings of the Auger group. The latest HiRes investigation is currently being reviewed by the Astrophysical Journal Letters, and could appear in an upcoming issue of this publication.