Active Galactic Cores As One Possible Source of The Particles
Interactions with blue-shifted cosmic microwave background radiation limit the distance that these particles can travel before losing energy; this is known as the Greisen–Zatsepin–Kuzmin limit or GZK limit.
The source of such high energy particles has been a mystery for many years. Recent results from the Pierre Auger Observatory show that ultra-high-energy cosmic ray arrival directions appear to be correlated with extragalactic supermassive black holes at the center of nearby galaxies called active galactic nuclei (AGN). However, since the angular correlation scale used is fairly large (3.1 degrees) these results do not unambiguously identify the origins of such cosmic ray particles. The AGN could merely be closely associated with the actual sources, for example in galaxies or other astrophysical objects that are clumped with matter on large scales within 100 Mpc.
Additional data collection is important for further investigating possible AGN sources for these highest energy particles.
Some of the supermassive black holes in AGN are known to be rotating, as in the Seyfert galaxy MCG 6-30-15 with time-variability in their inner accretion disks. Black hole spin is a potentially effective agent to drive UHECR production, provided ions are suitably launched to circumvent limiting factors deep within the nucleus, notably curvature radiation and inelastic scattering with radiation from the inner disk. Low-luminosity, intermittent Seyfert galaxies may meet the requirements with the formation of a linear accelerator several light years away from the nucleus, yet within their extended ion tori whose UV radiation ensures a supply of ionic contaminants. The corresponding electric fields are small, on the order of 10 V/cm, whereby the observed UHECRs are indicative for the astronomical size of the source. Improved statistics by the Pierre Auger Observatory will be instrumental in identifying the presently tentative association of UHECRs (from the Local Universe) with Seyferts and LINERs.
Read more about this topic: Ultra-high-energy Cosmic Ray
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