PhD Thesis Defense by Jacob Svensmark

The defence is held online via zoom. See guidelines and information here

Supervisor: Steen H. Hansen

External examiners: Darach J. Watson, Jeffrey Pierce and Nabila Aghanim

Titel: On the nature of dark matter structures, and the growth of charged atmospheric aerosols

Abstract: In my thesis I have focused on two main categories of research: The nature of dark matter structures, and the effect of cosmic rays on terrestrial cloud formation. On the dark matter, I take two approaches to testing our standard model: First I measure the movement of dark matter in the Perseus galaxy cluster, and second employ the IllustrisTNG simulation to revisit the weak gravitational galaxy-galaxy lensing signal, which has recently been found in tension with ΛCDM. In both cases I find my observations to be consistent with the standard model. On the influence of cosmic rays on cloud formation: It turns out that atmospheric ions produced by cosmic rays accelerate the growth of aerosols towards sizes where they can effect terrestrial clouds. This is demonstrated in both a laboratory experiment and a numerical model. If this accelerating mechanism works in Earth's atmosphere, cosmic rays from the Milky Way could potentially be affecting clouds, which is a climate mechanism unaccounted for at present.