How do weak shocks accelerate high energy particles?

Shock waves are found everywhere in the Universe and are one of the most efficient ways of accelerating particles like protons and electrons. However, the conditions required to produce those shocks and accelerate particles are so extreme that they're impossible to recreate on Earth. As a result, we still don't know a lot about how these shocks accelerate particles or how they're affected by things like density or magnetic field. Most of the shocks that produce these very high energy particles are also incredibly far away in other galaxies, making them difficult to study properly. For example, while we can see a supernova shock using astronomical telescopes, it's really hard to then identify and study the particles it accelerates.

However, the Earth is located close to a natural laboratory with extreme density, temperature and magnetic field variations which regularly produces large-scale shocks that shower us with energetic particles; the Sun. We have a fleet of spacecraft returning constant observations of the Sun, allowing us to see in near-real-time the sudden release of stored magnetic energy in the solar atmosphere (also called the corona). This energy release can produce bursts of radiation that we call solar flares, hurl massive bubbles of plasma called coronal mass ejections into the solar system towards the Earth and launch vast global shock waves that can travel across the Sun in under an hour. Although these shocks are so much weaker than supernovae that they shouldn't be able to accelerate any particles, they regularly produce billions of energetic particles that we can almost immediately detect at Earth. These particles can be fatal for satellites orbiting the Earth, blinding them and causing them to fail, with knock-on effects for GPS and telecommunications. With my research, I'm trying to understand why these really weak shocks occur, how they accelerate particles to incredibly high energies and how those energetic particles affect the Earth and the near-Earth environment.

The Sun offers a unique opportunity to study both extreme shocks and the particles that they accelerate at the same time in unprecedented detail; we can see what happens and "touch" the resulting particles, which is something that you can't do in any other field of astrophysics. Everything about this situation is also very counterintuitive; the Sun is a pretty average star producing very weak shocks that shouldn't be able to accelerate any particles yet it manages to accelerate particles to incredibly high energies. How this happens is still an open question, and one that has implications not just for our understanding of the Sun, but also for fundamental plasma physics and space weather. If we know how this process works we might be able to predict it, which will help us to protect vulnerable spacecraft and infrastructure on Earth. On a more personal level though, working on this topic really hammers home the differences between how calm the Sun is when you look at it from the ground versus the violently active Sun producing solar eruptions which we see from space, which I just think is fascinating.