Quasar. Artwork of jets emerging from the centre of a quasar. Many billions of times brighter than stars, they are thought to be galaxies centred around black holes. The brightness is believed to be caused by matter heating up and glowing as it falls into the black hole. The jets are thought to be gas which falls towards the centre of the quasar but is then redirected by strong electromagnetic fields and ejected at close to the speed of light.