Black holes give off light. Venture beyond the event horizon and you’ll not be able to escape the powerful gravity of a black hole. Black holes are objects so dense that not even light can escape their gravitational pull. Yet despite this, black holes can shine brightly, and this may be one of the most contradictory-sounding facts about space on our list. Supermassive black holes can illuminate the centre of galaxies and are known as active galactic nuclei. How can this be? As cosmic material falls into a black hole, it forms an accretion disc that swirls around it. This material gets very hot and glows: it can even power jets of material that shoot out of the black hole into space. This all occurs just outside the event horizon and is one of the ways astronomers can detect black holes even though they can observe them directly.