We’ve searched for decades for concrete evidence of intermediate-mass black holes, black holes with masses between 100 and 100,000 times that of the Sun. In spite of our best efforts, these monsters have remained elusive — but a new study provides some hope.
Searching for the Middle Sibling
Illustrations of two types of accreting black holes: a stellar-mass black hole accreting from a binary companion (top) and a supermassive black hole accreting gas in a galaxy’s center (bottom). [Top: ESA/NASA/Felix Mirabel; Bottom: ESO/M. Kornmesser]Work over the past 25 years has well established the existence of supermassive black holes — heavyweights with millions to tens of billions of solar masses — lurking in the centers of galaxies. Similarly, dynamical measurements and gravitational-wave observations provide compelling evidence of stellar-mass black holes, black holes with ~10 solar masses.
But what about the range in between? Theory predicts that intermediate-mass black holes should be the building blocks for larger supermassive black holes, but we’ve yet to find concrete evidence for a black hole with a mass between 100 and 100,000 solar masses.
To Weigh a Black Hole
We have, however, found candidates! A number of observational clues have pointed to hidden middleweight black holes ...