The hypothetical sources of EECR are known as Zevatrons, named in analogy to Lawrence Berkeley National Laboratory 's Bevatron and Fermilab 's Tevatron, and therefore capable of accelerating particles to 1 ZeV (10 eV, zetta-electronvolt). In 2004 there was a consideration of the possibility of galactic jets acting as Zevatrons, due to diffusive acceleration of particles caused by shock waves inside the jets. In particular, models suggested that shock waves from the nearby M87 galactic jet could accelerate an iron nucleus to ZeV ranges. In 2007, the Pierre Auger Observatory observed a correlation of EECR with extragalactic supermassive black holes at the center of nearby galaxies called active galactic nuclei (AGN). However, the strength of the correlation became weaker with continuing observations. Extremely high energies might be explained also by the centrifugal mechanism of acceleration in the magnetospheres of AGN, although newer results indicate that fewer than 40% of these cosmic rays seemed to be coming from the AGN, a much weaker correlation than previously reported. A more speculative suggestion by Grib and Pavlov (2007, 2008) envisages the decay of superheavy dark matter by means of the Penrose process.