Seven years ago, an outburst in a distant galaxy brightened and faded away. Afterwards, a new supermassive black hole jet emerged, but how?
At the center of practically every galaxy lies a supermassive black hole. The one in our Milky Way is about four million times the mass of our Sun, but others can be billions or even tens of billions of solar masses. Most of the time, these black holes are quiet: simply gravitating as matter orbits around them. But every once in a while, some object or collection of objects passes too close by the black hole, and the black hole begins to feed on that matter: heating it, accelerating it, and launching jets of particles and radiation. Overall, what gets emitted is so energetic, it can be detected from all across the Universe, with active galaxies and quasars among the most distant objects ever discovered.
These periods of activity can endure for long periods of time: tens of millions, hundreds of millions, or even more than a billion years (in at least one case), or far longer than humans have been observing the Universe. Up until recently, we had never witnessed a supermassive black hole in an active galaxy either “turn on” or “turn off” before, but a 2018 event changed…
