In this false colour image the two emission lines of oxygen gas (the weaker one at 4959 Angstroms and the stronger one at 5007 Angstroms) are clearly visible. The horizontal line passing through the image is from the light generated by the powerful black hole at the center of NGC 4151.

Credit: John Hutchings (Dominion Astrophysical Observatory), Bruce Woodgate (GSFC/NASA/ESA), Mary Beth Kaiser (Johns Hopkins University), Steven Kraemer(Catholic University of America), and the STIS Team