Did you know that light can bounce off a charged particle like an electron? And that this interaction can lead to some of the highest-energy gamma-ray radiation that we have ever observed in the universe? In this double blog post, I will build up an intuitive and visual understanding of how this quantum billiards between light and charged particles works (part 1) and how its relativistic version can explain some of the most fascinating astrophysical ultra-high-energy observations (part 2). Recently, the astrophysical community is flooded by exciting new observations from the Large High Altitude Air Shower Observatory (LHAASO) and High Altitude Water Cherenkov Experiment (HAWC). Both detectors are measuring light…

With the advent of the Christmas time, it is common to put yourself a nice candle in the living room (or sometimes even four or more). It is particularly nice to enjoy the warm and dim orange light, softly flickering and creating a cozy atmosphere. As an astrophysicist researching the light emission from outflows moving at almost the speed of light towards us, I was wondering what would happen to such a Christmas candle if I would do the same thing to the candle – move it at the speed of light. Clearly, the airstream would blow out the candle and it wouldn’t burn if we put it into a…