Astronomers have observed the largest explosion yet in space that we're aware of, a years-long event involving a supermassive black hole estimated to be one billion times more massive than the Sun that continues to rage.The eruption, codenamed AT2021lwx, was first recorded by ground-based telescopes - the Zwicky Transient Facility in California, and the Asteroid Terrestrial-impact Last Alert System in Hawaii - in 2020.