How to weigh a quasar

We have successfully tested the performance of a new method for determining the masses of extreme black holes in quasars, called spectroastrometry, for the first time through observations. It measures radiation coming from gas in the vicinity of supermassive black holes. Compared to other weighing techniques, it is relatively straightforward and efficient to perform using modern large telescopes. Its high sensitivity makes it possible to study the surroundings of luminous quasars and supermassive black holes in the early Universe.