Holm 15A and the most massive black hole in the local universe

Which galaxies harbour the most massive black holes? Even though galaxies tend to get more luminous towards their centres, the most massive galaxies exhibit a deficit of stars in their centres. The giant galaxy Holm 15A exhibits a particularly large deficit, and in this galaxy, we found a 40-billion-solar-mass black hole – the most massive known today. The faint centres of giant galaxies thus are an important indicator for the mass of their black hole – potentially even at distances, where direct measurements are not possible today.