A black hole under investigation is so hidden that it requires highly sensitive observations in the highest energy X-rays to classify it as obscured. But they give themselves away when material they feed on emits high-energy X-rays that NASA's NuSTAR (Nuclear Spectroscopic Telescope Array) mission can detect. That's how astronomers used NuSTAR to recently identify a gas-enshrouded supermassive black holes located at the center of a nearby galaxy IC 3639 some 175 million light years from Earth.