Astronomy Colloquium

The earth has been bombarded by high-energy particles for millions of years. Known as cosmic rays, these particles can have higher energies than particles accelerated by the best human-made accelerators. Since the discovery of cosmic rays in 1912, we have studied these energetic particles for over a hundred years. These particles should be accelerated under a more extreme environment than our Sun to obtain their high energies. Supernova remnants have been the most supported candidates to be our Galaxy's main sources of cosmic rays. However, it is challenging to study the sources of these particles because of the deflection of their trajectories by magnetic fields and their interactions with particles and radiation in interstellar and intergalactic space. Observations of the neutral particles, such as gamma rays and neutrinos, produced during the interactions experienced by cosmic rays have been expected to provide the key measurements to find the elusive source sites of cosmic rays. In recent decades, we have seen great improvements in cosmic-ray and gamma-ray measurements. High-energy gamma-ray observations have discovered over 200 astrophysical objects emitting gamma rays with energies higher than 100 GeV, while cosmic-ray measurements have revealed many unexpected features in the spectrum and composition. I will present an overview of current high-energy cosmic-ray and gamma-ray observations of our Galaxy, and a glimpse into future perspectives.

To view this talk on YouTube, please visit: https://www.youtube.com/playlist?list=PLb1880Rn0qkKFkWyROUq1kRlgCsuBTrnd

Super-Earths and sub-Neptunes are the most abundant exoplanets discovered to date. Recent models of atmospheric evolution and erosion by core-powered mass loss and photoevaporation suggest that these two populations of exoplanets might have been born as one. In these models, close-in, lower-mass planets lose their hydrogen–helium envelopes and become rocky super-Earths, whereas more massive, longer-period planets retain primordial H/He envelopes and remain sub-Neptunes. In my talk, I will explore the question as to how primary, hydrogen-rich atmospheres influence the physical evolution and chemical composition of super-Earths and sub-Neptune exoplanets and show that Earth's water, core density deficit, and overall oxidation state can all be sourced to equilibrium between hydrogen-rich primary atmospheres and underlying magma oceans in its progenitor planetary embryos. Reaction with hydrogen atmospheres thus provides a simple explanation for fundamental features of Earth's geochemistry that is consistent with rocky planet formation across the galaxy. 

To view this talk on YouTube, please visit: https://www.youtube.com/playlist?list=PLb1880Rn0qkKFkWyROUq1kRlgCsuBTrnd

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