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1. Cosmic Crashes

   Evans, Aaron S.; Armus, Lee (December 2021, Scientific American)

   Moskowitz, Clara (Ed.)

   Galaxy Collisions Preview Milky Way’s Fate New revelations about how galaxies collide show what might happen when our galaxy meets Andromeda 

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2. CHAMP cosmic rays

   https://doi.org/10.1088/1475-7516/2019/07/015  

   Dunsky, David; Hall, Lawrence J.; Harigaya, Keisuke (July 2019, Journal of Cosmology and Astroparticle Physics)
3. Cosmic axion background

   https://doi.org/10.1103/PhysRevD.103.115004  

   Dror, Jeff A.; Murayama, Hitoshi; Rodd, Nicholas L. (June 2021, Physical Review D)
4. The cosmic-ray staircase: the outcome of the cosmic-ray acoustic instability

   https://doi.org/10.1093/mnras/stac1123  

   Tsung, Tsun Hin Navin; Oh, S. Peng; Jiang, Yan-Fei (April 2022, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Recently, cosmic rays (CRs) have emerged as a leading candidate for driving galactic winds. Small-scale processes can dramatically affect global wind properties. We run two-moment simulations of CR streaming to study how sound waves are driven unstable by phase-shifted CR forces and CR heating. We verify linear theory growth rates. As the sound waves grow non-linear, they steepen into a quasi-periodic series of propagating shocks; the density jumps at shocks create CR bottlenecks. The depth of a propagating bottleneck depends on both the density jump and its velocity; ΔPc is smaller for rapidly moving bottlenecks. A series of bottlenecks creates a CR staircase structure, which can be understood from a convex hull construction. The system reaches a steady state between growth of new perturbations, and stair mergers. CRs are decoupled at plateaus, but exert intense forces and heating at stair jumps. The absence of CR heating at plateaus leads to cooling, strong gas pressure gradients and further shocks. If bottlenecks are stationary, they can drastically modify global flows; if their propagation times are comparable to dynamical times, their effects on global momentum and energy transfer are modest. The CR acoustic instability is likely relevant in thermal interfaces between cold and hot gas, as well as galactic winds. Similar to increased opacity in radiative flows, the build-up of CR pressure due to bottlenecks can significantly increase mass outflow rates, by up to an order of magnitude. It seeds unusual forms of thermal instability, and the shocks could have distinct observational signatures, on ∼kpc scales. 

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5. The Cosmic Lithium Story

   https://doi.org/10.2138/gselements.16.4.241  

   Lodders, Katharina (August 2020, Elements)

   Lithium’s story spans the history of the universe and is one that links to all its largest-scale processes: big bang nucleosyntheses, the evolution of stars, and galactic chemical evolution. Lithium was the only metal produced in the big bang, alongside the gases H and He. Stars destroy both stable isotopes of Li easily, yet we still have Li today, even after generations of stars have come and gone. Ongoing production of Li by galactic cosmic rays and by a limited number of Li-producing nuclear reactions and transport processes in some rare types of stars keeps lithium present in the universe. 

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