Supermassive black holes may provide a nursery for mini ones to grow

Thousands of relatively small black holes may be circling the supermassive black holes that lurk at the centres of galaxies. The idea would not only help explain how small black holes grow larger, it would also give us a new understanding of why supermassive black holes appear so bright.

The centres of galaxies are extraordinarily dense, so matter – including relatively small, or stellar-mass, black holes – tends to accumulate there. Some of…