We re-examine the possibility of ultrahigh energy cosmic rays being accelerated in nearby dormant quasars. We particularize our study to heavy nuclei to accommodate the spectrum and nuclear composition recently reported by the Pierre Auger Collaboration. Particle acceleration is driven by the Blandford-Znajek mechanism, which wires the dormant spinning black holes as Faraday unipolar dynamos. We demonstrate that energy losses are dominated by photonuclear interactions on the ambient photon fields. We argue that the local dark fossils of the past quasar activity can be classified on the basis of how source parameters (mass of the central engine and photon background surrounding the accelerator) impact the photonuclear interaction. In this classification it is possible to distinguish two unequivocal type of sources: those in which nuclei are completely photodisintegrated before escaping the acceleration region and those in which photopion production is the major energy damping mechanism. We further argue that the secondary nucleons from the photodisintegrated nuclei (which have a steep spectral index at injection) can populate the energy region below "the ankle" feature in the cosmic ray spectrum, whereas heavy and medium mass nuclei (with a harder spectral index) populate the energy region beyond "the ankle", all the way to the high energy end of the spectrum. In addition, we show that five potential quasar remnants from our cosmic backyard correlate with the hot-spot observed by the Telescope Array.
Spaceflight has been documented to produce a number of detrimental effects to physiology and genomic stability, partly a result of Galactic Cosmic Radiation (GCR). In recent years, extensive research into extremotolerant organisms has begun to reveal how they survive harsh conditions, such as ionizing radiation. One such organism is the tardigrade (Ramazzottius varieornatus) which can survive up to 5kGy of ionizing radiation and also survive the vacuum of space. In addition to their extensive network of DNA damage and response mechanisms, the tardigrade also possesses a unique damage suppressor protein (Dsup) that co-localizes with chromatin in both tardigrade and transduced human cells and protects against damage from reactive oxygen species via ionizing radiation. While Dsup has been shown to confer human cells with radioresistance; much of the mechanism of how it does this in the context of human cells remains to be elucidated. In addition, there is no knowledge yet of how introduction of Dsup into human cells can perturb cellular networks and if there are any systemic risks associated. Here, we created a stable HEK293 cell line expressing Dsup via lentiviral transduction and confirmed its presence and its integration site. We show that Dsup confers human cells with a reduction of apoptotic signals. Through measuring these biomarkers of DNA damage in response to irradiation longitudinally along with gene expression analysis, we were able to demonstrate a potential role for Dsup as DNA damage response and repair enhancer much in the same way its human homologous counterpart HMGN1 functions. Our methods and tools provide evidence that the effects of the Dsup protein can be potentially utilized to mitigate such damage during spaceflight.
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