Some black holes grow much faster than their galaxies

This artist’s impression depicts a rapidly spinning supermassive black hole surrounded by an accretion disc. Credit: ESO, ESA/Hubble, M. Kornmesser

Nearly every galaxy has a supermassive black hole. The few that don't have had theirs ejected during a galactic collision. That's because galaxies and their black holes have formed hand in hand. There is still some debate as to whether galaxies formed around the seeds of supermassive black holes or the other way around, but there is plenty of evidence to support the idea that the two evolve together.

One point of evidence is the fact that supermassive black holes generally have about 0.5% of a galaxy's mass. The mass correlation between black holes and galaxies suggests a strong connection in how they form. In the same way, the correlation between the size of a city and the number of people who live there suggests a connection between structural size and population.

But a recent study found oversized galactic black holes, challenging our understanding of their evolution. For this study, published in Astronomy & Astrophysics, the team used the eROSITA X-ray telescope and other observations to look at more than 20,000 quasars. Quasars are powered by active supermassive black holes.