That's a really tough question. There is a couple things that stand out, but they're not exactly astronomical things, just things I know because of astronomy. The evidence of the Higgs boson was pretty cool, although very sensationalized, when it happened I took to understanding what exactly that meant, which snowballed into me attempting to teach myself particle physics. What I found profoundly interesting is GUT, or Grand Unification theory, which basically posits that all the forces except gravity were once united, and split due to the expansion of space lowering the energy density, and entropy causing random fluctuations which cause supersymmetry breaking, or SUSY breaking for short. Now here's the issue, the Higgs boson is much much lighter than the GUT energy. Which what the means in English is that the strength of the force of gravity is a lot weaker than the weak force for no real reason. This issue is called the hierarchy problem. This interests because I think this could lead to the removal of gravity as a fundamental force, and instead of a by-product of another mechanism. Such as the Higg's mechanism which causes soft-SUSY breaking in the electroweak interaction to give particles mass. If we can find a mechanism which can be deduce to equal Newton's constant, we don't need gravity as a fundamental force.