All About Space

How big is a black hole? How messily it ‘eats’ may be a clue


- Words by Meghan Bartels

Scientists have long noticed flickering patterns in the brightness of accretion discs, rings of matter pulled in by black holes’ gravity. But researcher­s weren’t sure what caused the flickering. But by studying dozens of known supermassi­ve black holes, a team of astrophysi­cists has determined that the flickering of an accretion disc relates to the mass of the black hole swathed inside it – and the scientists believe that the same technique also applies to much smaller objects as well.

“These results suggest that the processes driving the flickering during accretion are universal, whether the central object is a supermassi­ve black hole or a much more lightweigh­t white dwarf,” said Yue Shen, an astronomer at the University of Illinois Urbana-Champaign.

To examine any connection between black hole size and the flickering light of the disc it feeds from, the scientists began by selecting 67 of these behemoths, each with a previously estimated mass between 10,000 and 10 billion times that of our Sun. Supermassi­ve black holes are much larger than stellar black holes, which form from a single star exploding and have masses three to ten times that of our Sun.

When the data seemed to show a correlatio­n, researcher­s decided to look at smaller objects with accretion discs as well: white dwarfs, which are the much smaller dense remnants of stars like our Sun that have exploded. The scientists hope that the same relationsh­ip will hold for objects with masses between these two classes.

 ??  ?? Above: Accretion discs could be the clue to weighing black holes
Above: Accretion discs could be the clue to weighing black holes

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