Stanford University astrophysicist Julie Hlavacek-Larrondo led a team that used data from NASA’s Chandra X-ray Observatory to analyze 18 of the universe’s brightest galaxy clusters, thought to be home to the biggest black holes. They found black holes larger than any discovered before: Ultramassive black holes with a mass 10-40 billion times the mass of our own sun. And those estimates might be on the small side. Says Hlavacek-Larrondo, “Some of our black hole mass predictions are just lower limits, so they could be higher… Just how big do I think they can get? I would bet that a least one 100-billion-solar-mass black hole exists among our objects, which really is ultra-big.” Hlavacek-Larrondo and company estimated the size of these ultramassive black holes by analyzing the X-rays and radio waves generated by black holes when they destroy the gas, dust, and stars that have the bad luck to come near them.