Scientists have witnessed the birth of a massive black hole at the centre of a galaxy for the very first time. In late 2019 the previously unremarkable galaxy SDSS1335+0728 suddenly started shining brighter than it ever had before - prompting interest from astronomers. To understand why it was shining, astronomers have used data to track how the galaxy’s brightness has varied. In a new study they conclude that they are witnessing changes never seen before in a galaxy — likely the result of the sudden awakening of the massive black hole at its core. “Imagine you’ve been observing a distant galaxy for years, and it always seemed calm and inactive,” says Paula Sánchez Sáez, an astronomer at ESO in Germany. “Suddenly, its core starts showing dramatic changes in brightness, unlike any typical events we've seen before”. SDSS1335+0728 is now classified as having an ‘active galactic nucleus’ after it brightened dramatically in December 2019. Some phenomena, like supernova explosions can make galaxies suddenly light up. But these brightness variations typically last only a few dozen or, at most, a few hundreds of days. SDSS1335+0728 is still growing brighter today more than four years after it was first seen to ‘switch on’.