A relativistic jet is a narrow beam of plasma launched at close to the speed of light from the neighborhood of a compact object, usually a spinning black hole or neutron star. Magnetic fields anchored in the accretion disk twist into a helix that collimates the outflow and hurls it outward, sometimes for hundreds of thousands of light-years. Jets from supermassive black holes can extend far beyond their host galaxy and reshape the gas around it. The one emerging from M87 was photographed decades before the black hole that launches it was imaged.