Yes, it's back -- after a two-year upgrade program, CERN's Large Hadron Collider is once again operational. Scientists are only firing collision-free proton beams right now to test the new system, but they'll ramp up over the next few months to the point where they're smashing protons together at 13 teraelectronvolts -- about twice the energy the LHC managed in its first season. The machine will have a relatively short three years to operate before its next shutdown, but the higher output should help researchers explore antimatter, dark matter and other aspects of physics that are relatively untested. Given that the collider appears to have discovered the mysterious Higgs boson during its first run, we're hopeful that its second season has more breakthroughs in store.

[Image credit: CERN]