We know the universe is constantly expanding. We also know that gravitationally bound objects, such as solar systems and black holes, seem to be immune to that expansion. But a new paper by theoretical physicists Valerio Faraoni and Massimiliano Rinaldi challenges that assumption. They suggest that black holes can't just ignore the expanding universe around them. Instead, they have to expand along with it. Their paper is posted to the arXiv preprint server.