Gamma-ray bursts are the most violent explosions in the Universe. The most distant gamma-ray burst ever observed occurred when the Universe was only 600 millions years old (it is 13.6 billions years old today). At that time, our Galaxy, the Milky Way, was not yet even formed and nor were the Sun and the Earth! Gamma-ray bursts are characterised by short (a few milliseconds to a few hundreds of seconds) and intense flashes of X-ray and gamma-ray light. They appear randomly across the sky and in time. They are likely associated with the catastrophic formation of black holes (i.e celestial bodies that are so extreme that even light cannot escape, hence their name!), when massive stars collapse at the end of their life due to their extreme gravity or when two neutron stars orbiting each other finally merge. During these catastrophic events, matter falls onto the recently formed black hole and a fraction of this matter is ejected in the form of jets / winds creating a powerful beam of light. If the beam is oriented toward the Earth, an observer will see a gamma-ray burst.