You might not be able to tell from wherever you are reading this, but black holes in the distant universe just shrunk down to as little as a tenth of their previous size. This is not some cosmic disappearing act; a new analysis of supermassive black holes at the centres of active galactic nuclei has revealed that their masses were previously overestimated by up to a factor of ten. The paper was published in Nature last week.



Active galactic nuclei, or AGN, are among the most luminous objects in the universe and are powered by massive black holes millions of times the mass of the Sun. Gas clouds, known as “broad line regions” for reasons that will become clear later, surround the black holes. These gas clouds range from a few light daysto hundreds of light days across; they are much wider than our solar system. Astronomers have been studying these clouds for over thirty years, but had not worked out the why some of them were flatter than others — until now.

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