Astronomers have detected an enormous black hole - the second-heaviest ever seen - but it resides in a tiny galaxy.
The galaxy NGC 1277, which is just a quarter the size of the Milky Way, hosts a black hole 4,000 times larger than the one at the Milky Way's centre.
A report in Nature shows it has a mass some 17 billion times that of our Sun and comprises 14% of the entire galaxy's mass.
The BBC science correspondent says the finding is hard to reconcile with existing models of black hole growth, which hold that they evolve in tandem with host galaxies.
"This galaxy seems to be very old," Dr Van den Bosch of the Max Planck Institute for Astronomy in Germany told BBC News.
"So somehow this black hole grew very quickly a long time ago, but since then that galaxy has been sitting there not forming any new stars or anything else.
"We're trying to figure out how this happens, and we don't have an answer for that yet. But that's why it's cool."
