This illustration compares the environment around NGC 4151's supermassive black hole with the orbits of the planets in our solar system — the planets themselves are not shown to scale. Echoes of X-ray flares detected in XMM-Newton data demonstrate that the X-ray source (blue sphere, center) is located above the black hole's accretion disk. The time lag between flares in the source and their reflection in the accretion disk places the X-ray source about four times Earth's distance from the Sun. Credit: NASA's Goddard Space Flight Center