Accretion discs show their true colours

Artist's impression showing the principle followed by the team to uncover the true colour of the quasars' disc. The red star-like object in the upper left panel is one of the quasars observed. The light is thought to originate from an accretion disc around a black hole with a strong contamination from messy dust clouds, as shown by the drawing on the upper-right panel. When the astronomers put a polarising filter in, these clouds are suppressed from view, giving us the true colour of the accretion disc, as shown in the two lower panels. Some of the quasars have a very small amount of scattered light coming from the vicinity of the black hole itself, rather than the clouds of gas and dust around it. This light has become polarised after hitting matter within the disc. By using a filter that only allows this polarised light to come through and blocks out the unpolarised light from the gas clouds, they were able to visually eliminate them and reveal the disc. Figure by M. Kishimoto, with cloud image by M. Schartmann.